1220-1225Fish diversity and abundance were investigated at reefs around Royal Thai naval base, Sattahip area. A total of 46 species in 17 families were recorded in the area. Hin Luk Bet had the highest number of fish species (32 species) while the lowest number of fish species was found at Ko Kham (14 species). Most abundance families were Pomacentridae followed by Chaetodontidae and Labridae. The results from the Jaccard similarity index showed that the similarity index was ranged between 0.3-0.6. Highest similarity was found between at Ko Kham and Ko Tao Mo. This is the first report on the diversity and abundance of fish species in the Royal Thai naval base