Abstract: The Sox genes family comprises several transcription factors that share a highly conserved HMG (High-Mobility-Group) box and has been studied in many species, including a variety of vertebrates and several of invertebrates such as fruit fly, nematode and Portunustrituberculatus. But there are only few reports on Sox gene family of freshwater bivalve so far, which have important value in evolution and production. H. schlegelii, which originated from Lake Biwa in Japan and was introduced into China in 1998, is one of the representative freshwater pearl mussels. It has been widely applied in the Chinese freshwater pearl industry for its high quality pearl bearing ability. In order to know the function of Sox genes in this mussel, a degenerate PCR, referred to the HMG box of human SRY gene, was used to amplify the conserved sequence of HMG domains of Sox genes. Two different HMG sequences were got from DNA and the testis cDNA, named DNA-HMG1, DNA-HMG2 and cDNA-HMG. Amino acids sequences analysis showed that those HMG sequences had high homology with the Sox1, Sox2, Sox3 and Sox14 genes from other animals including human being. But there showed no difference between the male and female. A partial cDNA sequence of Sox2 gene (refereed as hs-Sox2) with 1774 bp including partial ORF and complete 3' untranslated region (UTR) was cloned from the testis cDNA by RACE-PCR methods. DNA sequences analysis showed that it had high homology with the SoxB gene in Patella vulgata and the Sox2 gene in human being. The putative 249 amino acid sequence contained one conserved HMG box like the human SYR gene, and exhibited 98% homology with human, mouse, chicken and zebrafish. For further know the expression level of Sox2 gene, real-time PCR method was used to examine its mRNA level in different tissues and different months on testis of H. schlegelii. Results showed that the hs-Sox2 mRNA was ubiquitously expressed in all the tissues, with the highest in kidney, followed by intestine, adductor muscle, and the expression level in the testis was higher than that in the ovary. The result from the different months on testis revealed that hs-Sox2 was transcribed mainly in the 39 months, followed by 16 months and lowly in the 63 months. These results suggested that hs-Sox2 may be involved in the development of on testis in the H. schlegelii and may constitute clues for future work in order to better understand Sox protein.