Sox genes are a family of genes that encode proteins which are characterized by the presence of a HMG-box related to that of the mammalian sex-determining gene SRY. By definition, the DNA binding domain of Sox genes is at least 50% identical to the 79 amino acids HMG-box of the SRY gene. Sox genes are highly conserved throughout evolution, from human to Drosophila . In the present study, using degenerate primers which specially amplify the conservative motif of human SRY gene, the PCR amplification of Sox gene in genomic DNA of the mud crab Scylla serrata was studied. The result showed that only one band was present in the PCR products of Scylla serrata, and the length was 216bp, equal to that of human SRY gene, but no difference between male and female. These may be concluded that Sox genes are highly conservative in phylogenetics. The present paper provides molecular data for the study of sex-determining mechanism of Scylla serrata or other shrimps and crabs, and for the evolution of Sox genes.