Abstract: The RAPD analysis of Streptococcus iniae virulent strain DGX07 isolated from channel catfish(Ictalurus punctatus)was conducted by PCR with Primer p14(5′-GATCAAGTCC-3′).The simA gene of DGX07 was amplified by PCR with specific primers and cloned into pMD19-T vector.The positive plasmid was selected and identified by PCR and digestion of double restriction enzyme(BamHⅠ+XhoⅠ).Molecular characterization analysis of simA gene was performed by bioinformatics tools.The results showed that S.iniae simA amino acid sequence was highly conservative and with 100% homology to the simA and simB of S.iniae isolated.The polypeptide contained a signal peptide comprising 41 amino acids and Bap31 and Gram_pos_anchor functional domains.The polypeptide had some important sites related to post-translational modification,including 22 phosphorylation sites and 2 N--glycosylation sites.The hydrophilic regions were larger than hydrophobic regions in polypeptide chain.The S.iniae simA was extramembranous protein with multiple antigen advantaged regions.The analysis of codon bias indicated the codon usage frequency of S.iniae simA different,and the codon bias of S.iniae simA preferred the yeasts.Gene accession number:JF330100.