Holothurians (Class Holothuroidea, Phylum Echinodermata) of the Eastern Coast of  Thailand were intensively studied from the specimens collected from 4 marine habitats namely, coral reef, seagrass bed, sandy and rocky beaches in Chon Buri, Rayong, Chanthaburi and Trat Provinces from 1998 to 2002. In addition, museum specimens from the authors's collections also examined along with other specimens deposited in several institutions and collections in Thailand. The holothurians found were classified into 4 Orders, 6 Families, 14 Genera and 34 species. Regarding the observed habitats, it was found that there