The diversity of Epinephelus species was investigated throughout Thailand. Random amplified polymorphic DNA successfully produced 1300 bands that were phylogenetically informative and used to construct cladograms. Values of pairwise genetic similarity (S) within species ranged from 0.65 in E. erythrurus to 0.99 in E. malabaricus. The interspecific values of S ranged from 0.23 between E. malabaricus and E. bleekeri to 0.66 between E. coeruleopunctatus and E. erythrurus. The intraspecific nucleotide variation ranged from 0.037 to 0.159 in the mitochondrially encoded 16S RNA (MT-RNR2) region and from 0.003 to 0.157 for the mitochondrially encoded cytochrome c oxidase I (MT-CO1) region. All sequences were submitted individually to GenBank. The barcode sequences of Thai species of Epinephelus were aligned to the same species found in GenBank. For the MT-RNR2 gene region, intraspecific nucleotide variation ranged from 0.000 to 0.121, and interspecific nucleotide variation ranged from 0.003 to 0.146. For the MT-CO1 gene region, intraspecific nucleotide variation ranged from 0.000 to 0.140, and interspecific nucleotide variation ranged from 0.000 to 0.166. The MT-RNR2 data indicate that some species, including E. bleekeri from India and E. malabaricus from Thailand are not monophyletic. Additionally, the MT-CO1 data indicated that E. bleekeri, E. quoyanus and E. coeruleopunctatus are not monophyletic. The sequences of E. lanceolatus from each country are highly conserved, with genetic distances ranging from 0.000 to 0.003. Another important result from this study is that the barcode sequence from Thai E. erythrurus was previously not present in the GenBank.