Abstract: The Sox genes of Trionyx sinensis were amplified and cloned using PCR. The four different fragments of Sox gene HMG-box DNA were selected and sequenced. The results indicated that the Sox gene is conservative in phylogeny, in which the amino acid sequence encode by TSSox4(The Sox of T. Sinensis)is identical to those encode by LF4(bird)or differ from SOX4(human)and Sox4(mouse)only on one amino acid; The amino acid sequences encode by TSSox5 have an amino acid difference from those encode by LF5(bird); TSSox1 has about 75% identical to SRY HMG-box at the nucleotide level, and is most resemblance among four TSSox. Phylogenetic analysis of available 32 Sox sequences including SRY/Sry sequence suggests that there wolud be a high degree of divergence between any possible immediate common ancestor of the T. Sinensis Sox sequence and the SRY(Sry)sequences.