Koh Chang Marine National Park offers some of the most spectacular dive sites. The season starts from mid October to end of April. The best sites are on the west and south of Chang Island where the abundance of colourful and unspoiled corals and the great diversity of fish are the main draw.

Popular sites include Klong Son Beach, Yuak Island, Man Nai Island, Koh Man Nok, Larp Rock, Sam Sao Rock, Look Bard Rock, Run Taek Rock, Rom Island, Wai Island, Ngam Island, Rang Island, Laoya Island, Mai Si Lek Island, Raet Island, Mak Island, Kham Island, Rayang Yai Island, Kra Island, Thong Lang Island, Thian Island, and Yak Island.

Chang Noi Island is located off Chang Noi Cape at the northwestern tip of Chang Island. The island and the cape consist mainly of rocks and forest, but the beauty of this area lies in the seabed between with unspoilt virgin coral reefs. For advanced divers, there are several wrecks in the vicinity of Chang Island.

The "Koh Chang Wreck" is a Thai warship sunken by the French Navy. The wreck lies in shallow waters near the Salak Petch Bay, south of Chang Island.

The "Pak One" wreck is a 900-tonne tanker that was also called the Vertical Wreck. The ship sank after hitting a coral reef in August 1996 on its way to Vietnam. It resurfaced some years later and drifted bow-upwards into international waters, where it posed a danger to passing ships. The Thai Navy drained off its cargo of liquefied petroleum gas and re-sank it between Chang and Samet Island, where it lies horizontal, in 35 metre deep waters.

The "Hardeep" was sunk by Allied bombers during World War 2. The Indonesian cargo ship was used by the Japanese army to run supplies to Thailand where they were building the railway linking the country to Burma. It is 64 metres long and lies on its starboard side, a few hundred metres from Chuang Island, where the skipper made a vain effort to beach the ship. The hull is largely intact and access to the engine room is possible for experienced divers. The huge crankshaft and some fire bricks are still in place. The remnants of the funnel are resting on the seafloor in 28 metres of water with the foremast nearby. Carry a torch to examine dark corners, there is certainly a lot to be explored inside. After nearly 60 years nature has worked her magic on the wreck and it is home to angelfish, batfish, groupers, stingrays, barracuda, wrasse, butterfly fish, crabs, and nudibranches.

The "Bremen" is a 110-metre freighter severely damaged by a fire and an explosion in her engine room in the mid-1930s. The ship is in three main parts, while the forward and stern sections are relatively intact, the centre part is a tangle of steelwork caused by the explosion and by demolition practice carried out by the Royal Thai Navy. Penetrating the main hull sections is not advised, but the skipper's private bathroom, complete with bath, lavatory and very attractive ceramic floor tiles, can be explored by experienced divers. Nature has claimed the Bremen and many types of coral and sea whips grow on the sides and decks of the ship. Blue-ringed and six-banded angelfish, batfish, moray eels, rays, barracuda, and numerous smaller reef fish inhabit the wreck.