The Koh Chang Marine National Park is comprised of 52 islands, all of which are least exposed and best preserved in nature. Rich in rainforests, well-laden with colourful corals, abundantly stocked with healthy marine lives, encompassed by spectacular coastlines, gorgeous landscape, pristine beaches and crystal clear sea, a visit to these islands is a journey back to nature. Fresh, tranquil and laid-back, these islands are most worthy of a holiday. However, only 10 of these islands are facilitated with accommodation which range from the very basic thatched roof huts of USD 10 a room-night to the more luxurious and sophisticated properties that can cost as much as USD 100 a room-night. 
There are also many island resorts that accept only package tours of full board groups because of its exclusiveness and distance from the mainland. These are well-preferred by those who love isolations. They include boat transfers, full meals, some with side trips and usually at least 2 nights accommodation.
Most of the islands have limited or no development at all. Many of them are uninhabited.The following are some of the best favoured islands off the main island of Koh Chang beginning from the north, west and then south of Koh Chang.
KOH CHANG NOI - Laem Chang Noi 
Koh Chang Noi is an island off Laem Chang Noi (Chang Noi Cape) which is located at the northwestern tip of Koh Chang. The island is comprised mainly of rocks and forest whereas Laem Chang Noi is a cape of purely rocks with no vegetation at all. The beauty of this area lies in the seabed between them where you will find splendid unspoilt virgin coral reefs. Facing the island and cape is the new five-star resort known as the Aiyapura Resort & Spa which has well-appointed rooms with a splendid landscape and superb view.
KOH YUAK, KOH MAN NAI, KOH MAN NOK
Off the west coast of Koh Chang are a small group of islands delightfully visible especially from Klong Prao and Kai Bae beaches. These include Koh Yuak which has a small beachfront of sand formed from decayed corals. The water is clear and shallow qualifying it a good snorkeling spot.
From the shores of Klong Prao Resort the islands form a picturesque view especially during sunset. Next to Koh Yuak is Koh Plee and Koh Suwan, both of which have rocky shores. Around the area of Koh Suwan is an unnamed isle which is found to harbour colourful corals about 6 meters deep. Locals call this Koh Rom which means Umbrella Island because of an outstanding beautiful big tree with an umbrella shape. This is a new-found snorkeling site.
Further down south is Koh Man Nai which is directly facing the shores of Kai Bae Beach and very close to the Sea View Resort. The waters between Sea View Resort or Kai Bae Beach and Koh Man Nai is quite shallow. During the low tide when the island bare its lovely sandy beach one can actually walk amid chest-deep waters from the resort to the island.
Another island called Koh Man Nok looks as if it’s behind Koh Suwan. It is the twin island to Koh Man Nai and is linked together by shallow waters with plentiful of gold-coloured seaweed
KOH KHLUM 
Koh Khlum has a historical significance as the battleground between the French and the Thai navies during the French colonization of Indochina. It was also a shelter for the Thai naval forces. Koh Khlum is a good dive site especially at the Larn Hin area where you find corals at Hin Look Bard and Hin Larp which are about 10 to 20 meters deep. It is also a great fishing spot with an abundance of larger fishes.
KOH PHRAO or Koh Sai Khao 
This is a small island situated within Ao Salak Petch (Salak Petch Bay). Originally it was known as Koh Phrao because of the long lines of coconut trees on the island. Today, it is more commonly called Koh Sai Khao to reflect the abundance of fine white sand on the island. So abundant is the sand that a sand dune now extends to the sea and is particularly obvious during the low tide.Koh Sai Khao has a scenic view, clean clear seawater and is very serene. A concrete pavement by the seaside allows a pleasant stroll. One side of the island has a concrete bridge which stretches out into the sea and serves as a pier and a great view point. 
Koh Sai Khao Resort provides the only accommodation available on the island in the form of bungalow units. Only full board packages are available.
KOH LAOYA
Situated further south of Koh Sai Khao is a group of 3 small islands called Koh Laoya Nai, Koh Laoya Klang and Koh Laoya Nok. They are famous for their long white sandy beaches, sparkling clear seawaters, green forests and an amazingly beautiful coral settlement beneath the shallow, clear seawaters, particularly at Laoya Klang. A wooden bridge links the islands of Koh Laoya Klang to Koh Laoya Nai. Here, you will find the water beneath the bridge surprisingly transparent. There is only one resort here called Laoya Resort which accept only full board packages.
KOH WAI 
Koh Wai is a bigger island further south of Koh Laoya with huge bays. The beaches of Koh Wai is beautiful with reddish clean sand, some of which has corals right from the beach, especially the lump corals which are found to be large and in their best of conditions. The northern beach is the most popular due to its long sandy beachfront and healthy corals. Seawater are relatively shallow and snorkeling is a favourite activity as Koh Wai is blessed with a coral reef of up to 2 kms long. Encircling the island are many rocks making it a perfect fishing ground with a great quantity and variety of fishes. There are 2 accommodation to choose from, the Koh Wai Pakarang Resort offering full board packages and the Koh Wai Paradise Resort offering cheap and simple lodgings. Both are bungalow-style resorts.
KOH NGAM 
Koh Ngam is an enchanting island just a few hundred meters off the southern coast of Koh Chang. It is a small island with a very narrow sand dune that forms a gorgeous contour holding the northeast and southwest section of the island together. The almost kidney-shaped island would look like 2 separate islands from afar. Besides holding the island in one piece the sand dune created 2 crescent-shaped lagoons which are only 50 meters apart. The lagoons are excellent for swimming, snorkeling, diving, or fishing.Corals and fishes are aplenty. Occasionally, you may see dolphins in the area.For the more adventurous, a hike up the rocks to a 100 meter-tall hill on the southwest side of the island is both challenging and rewarding. Ropes are provided to guide you. Over the hill is a white sand beach where you will also see plenty of decayed corals. The beach is an excellent viewpoint for the islands of Koh Wai, Koh Mak, Koh Laoya, Koh Kradad and Koh Chang. It is also a great place to watch the sunset. Koh Ngam is ideal for a family vacation.
There is only one resort here, the Twin Island Resort , which offers only full board packages. Fresh-water ponds are found on the island. A waterfall flows across the island during the rainy season.
MOO KOH MAI SEE
This is a group of islands southwest of Koh Chang with unspoilt nature most suitable for swimming and fishing. The islands are made up of mostly mountains and forest with some coconut groves around the fishing villages. Koh Mai See Yai has a splendid sandy beach along its bay on the east.
KOH MAI DANG
A small island east of Koh Wai, Koh Mai Dang is peaceful and tranquil. It’s white sandy beaches and unspoilt corals are the main attractions. A great place to fish and camp
KOH KOOD Sub - district
A group of 24 islands south of Koh Chang was designated as the Koh Kood sub-district in 1990. These include the main island of Koh Kood, 9 islands of Koh Mak and 12 islands of Koh Rang. Koh Kood Sub-district has a very small population of less than 2,000. About 70% of the population are on Koh Kood while the rest live on Koh Mak. Almost all other islands are uninhabited. Fishing and agriculture are the main occupations.
Situated 80 kms southeast of the provincial capital of Trat, Koh Kood is the farthest island from the mainland. It is also the easternmost island of Thailand bordering Kampuchea. With an area of 129 sq. kms Koh Kood is the second largest island of the Koh Chang Marine National Park and fourth largest in Thailand, after Koh Samui. It is supported by essential infrastructure, which include a hospital, schools, police station, electricity (mainly for state-run facilities), water and telephone system. Fuel and solar energy are the main sources of electricity here. Most resorts generate their own electricity. 
The oldest village in Koh Kood is the Klong Mad Village where the people are of Thai and Cambodian origins. These early dwellers had migrated from neighboring Koh Kong since the turn of the 20th century during the French colonization of Indochina. Koh Kood has a mountainous terrain in the central region. About 70% of Koh Kood are covered by tropical rainforest. Development is scarce and mostly at coastal areas. Koh Kood boasts of scenic beauties, crystals clear sea, pristine beaches, breathtaking waterfalls and a very pure nature environment.
Boats from the piers in Laem Ngob and the Dan Kao pier on the mainland take about 4 ? to 5 hours to reach Koh Kood. Speed boats takes slightly over an hour. The resorts which cater to the higher priced market include this trip in their packages. There are several resorts, most of them are on the west coast. Koh Kood is little known to foreigners. Most of the visitors are Thais who find it a paradise. Most resorts have a minimum requirement on number of guests per package, usually 10. However, if you do not have your own group you can join the others to meet the minimum required.
The west coast is lined with a series of pristine beaches, sparkling clear sea, captivating views and is a great place to catch the magnificent sunset. Most of the best known beaches are along the bays which include the Ao Pak Waeng, Ao Klong Ta Tin, Ao Klong Yai Kee, Ao Tapow, Ao Klong Chao, Ao Klong Hin and Ao Prao. Noted fishing villages include the Ban Klong Mad and Laem Hin Dan. The famed Klong Chao Waterfall is situated further inland between Ao Klong Chao and Ao Tapow. This a fabulous waterfall with a large pool at its front. A 20-minute boat ride from the Klong Chao Bay plus a short hike lead to the fall. Alternatively, you can hike up the 4 kms trail.
The east coast is equally beautiful with fascinating views of the glorious sunrise. The prime areas include Ao Sapparos, Ao Klong Kwaen, Ao Yai Kerd, Ao Hin Yai and Ao Chak. Ao Salad and Ao Yai are the major fishing villages here. The Khao Paenthee is the highest hill and has just been recently discovered as a superb viewpoint for the sparkling island-dotted seas. 
Two of the most beautiful islands closest to the shores of Koh Kood are Koh Mai Si Lek and Koh Raet. Both are small islands of coconut trees, fine beaches, healthy corals and excellent sunset viewpoints
KOH MAAK
Lying between Koh Chang and Koh Kood, about 40 kms. from the mainland is a group of 9 islands called the Moo Koh Mak. Only 4 of these islands, including Koh Mak, Koh Kradad, Koh Kham and Koh Rayang Nok are occupied. Koh Mak, with an area of only 16 square kilometers and a 27 kms coastline, is the third largest island of the Marine Park. It has a flat terrain with plenty of coconut and rubber plantations. The main attractions are the long beaches and clear seawaters. There are only a few hundred people living here, most of them related. 
There are about 10 resorts mostly situated at the northwest or southwest of the island. Almost all the resorts are sold on full board packages with sightseeing trips and transportation. A good example is the Koh Mak Cococape Resort which offers a 3,800 Baht package that include 2 nights accommodation plus snorkeling trips to Koh Rang, Koh Kra and Koh Yak by speed boat or 2,800 Baht by fishing boat.
The main pier to Laem Ngob is the Ao Nid Pier, east of the island. Infrastructure is limited but there is a road system that conveniently link up the island. Ao Suan Yai, to the northwest has the longest and most beautiful beach where you can view Koh Raet, Koh Phee, Koh Kham as well as the captivating sunset. The beach is lined with lazy coconut trees.There are some fine restaurants here too. During low tide a sand dune appears between Koh Mak and Koh Kham allowing you to walk across. 
Ao Khao on the southwest is another spectacular site of fine beach with clear waters and great views of Koh Kood, Koh Rayang Nai, Koh Rayang Nok and the beautiful sunset. There are some reefs teeming with plentiful of fishes and is a favourite site for the anglers. 
KOH KHAM
Just 1 km. northwest of Koh Mak is Koh Kham, a small island with clear seawater, coral reefs and coconut-fringed sandy beaches that are excellent for swimming, snorkeling, fishing and angling for squids. Aged lava exist on the island which proves the existence of a volcano in prehistoric times. Big boulders believed to be volcano rocks are seen on its pristine beaches. During low tide a sand dune surface that links the island to Koh Mak and you can walk across to Koh Mak.
MOO KOH RANG
To the west of Koh Mak is a group of 12 islands known as the Moo Koh Rang. Of these, Koh Rang Yai is the largest. It is covered with tropical virgin rainforests and boast of the longest and most beautiful beach in the area, the Had San Chao or San Chao Beach, where the sand is powdery white and water crystal clear. Divers can enjoy its scenic underwater beauty up to 25 meters deep. 
Koh Rang Yai has a hilly terrain. Its only low-lying area are at the shores. Birds and reptiles are the main wildlife.Northwards from San Chao is Had Ao Cho or the Ao Cho Beach which is the site of a Marine National Park Ranger Unit. Here, the water is transparent and swimming is safe. Camping here is allowed at a small fee and with the approval of the officer in charge but you have to prepare your own food. Water supply and toilets are available. In front of the Ranger office is bridge made by dropping rocks and stones into the sea. The bridge was built to help transport supplies from the International Red Cross Organization to the Vietnamese refugees in the past.
Further south of Koh Rang Yai is Koh Rang Lek which is the main freshwater supplier to the former. There is a bird’s nest concession in Koh Rang Lek and it is also a major source of bat’s dung, which is known to be great fertilizers. Lucky visitors may see sea-turtles laying eggs on Koh Rang Lek and other nearby islets as they are found to be the chosen nesting grounds. The locals call them charamed eggs. The other well-known asset of Koh Rang Lek is its beautiful oval-shaped stones which has very smooth textures.
The islands of Koh Kra, Koh Thong Lang and Koh Thian on the northeast of Koh Rang Yai are great sites for skin diving. An array of varied corals and fishes abound. Of these islands, Koh Kra has the longest beach, although only 20 meters long. Swimming is not recommended here as the seabed is carpeted with corals. All these 3 islands are only walking-distances apart and the seawater is so shallow that it is possible to do so during low tide, but you should float with a life jacket or buoy to avoid stepping on some of the healthy corals.
The last coral island you should not forget is Koh Yak where you will virtually swim with the fishes while you snorkel. However, Koh Yak is a rock island with no beach. It is off the shores of San Chao Beach.