DNA Methyltransferase-2 (2) is one of the most widely distributed DNA methyltransferases in eukaryotes and plays important roles in eukaryotic development. In this study, the full-length cDNA of the Portunus trituberculatus) using rapid amplification of cDNA ends (RACE). The length of 2 cDNA is 1291 bp, and contains a 1203 bp open reading frame that is predicted to encode 400 amino acids. Structural domain analysis revealed that the protein of 2 contains a typical methyltransferase structural domain. Homology analysis revealed that the exhibits high identity with those in other species. Phylogenetic analysis showed that the amino acids of Macrobrachium rosenbergii. PtDnmt2 was found to be expressed in all tested tissues, and highly expressed in ovary and heart tissues (2 showed stage-specific expression during embryonic and larval development. No expression was detected in the zygote and multicellular stages. It was, however, detected from the blastula stage, after which expression increased gradually with embryonic development. Expression of 2 changed significantly during gonadal development. During ovarian development, the highest expression occurred in stage Ⅱ after which the level dramatically decreased. During testis development, the expression of 2 increased gradually and reached its peak in stage IV. The results suggest that 2 is important in the regulation of embryonic, larval, and gonadal development, and will provide useful information for further research on the roles of DNA methylation in developmental regulation in .