Genetic diversity of Epinephelus coioides (Hamilton, 1822), which inhabits coastal reefs from the western Indian Ocean to the western Pacific Ocean, was studied based on four polymorphic microsatellite loci. Two hundred and fifty individuals were collected from two locations in Thailand (Nakornsrithammarat-N and Trang-T) and four in Indonesia (Sibolga-S, Lampung-L, Jepara-J, and Flores-F). The genetic variation of E. coioides was relatively low; the observed heterozygosities (Ho) ranged between 0.36 (F) and 0.55 (N). The average number of alleles/locus was between 3.57 (L) and 5.09 (J). Genotypic distribution for most population pairs was significantly different after Bonferroni correction (P<0.0024) except for J and F. Population structuring was significant (FST=0.074). The genetic distances between populations ranged between 0.016 (L and N) to 0.086 (F and S). Mantel's test showed no correlation between genetic distance and geographical distance. The NJ tree clearly separated N from the others which comprised two subgroups, T-S and L-J-F.