In this study,we used RT-PCR to clone glutathione s-transferase (GST) fragments from Hyriopsis schlegerlii and H. cumingii. The two species had the same sequence which encoded a peptide of 92 amino acids. They shared high GST homology with mollusks,amphibian and mammals when comparing different spices at a polypeptide level. GST was detected in all tissues except for intestine,especially higher expression of GST in liver was observed. Result showed that the GST expression in haemocyte was declined at the first stage and then increased in H. cumingii,while its expression pattern was opposite in H. schlegerlii and the expression level of GST in the latter was approximately two times of that in H. cumingii at 3 h,6 h,9 h and 24 h after infection by Aeromonas hydrophila.