Abstract: ObjectiveTo clarity the character istics of mutations in HBV Snucleotides and amino acid sequences from the patients with chronic HBV infection,whose serum were detected both HBsAg and anti-HBs positive.MethodsA set of specific primers were synthesized according to HBV DNA sequence of adr subtype,the whole S,gene was amplified from the serum of two patients and the PCR products were subcloned into pGEMT easy vectors.Sequence comparison was made between the target sequence from the HBsAg/anti-HBs positive serum and that from HBsAg positive serum.ResultsSequencing results proved the high consistency,with only 4 out of 1428 nt(0.3%)were different between the target sequence from the double positive serum and that from the HBsAg positive serum,but with no specific amino acid site difference in PreS1,PreS2 and major protein.There were 3 sites of difference in spacer region corresponding to HBV polymerase.Conclusion There were HBV quasispecies in the patients with chronic HBV infection.The phenomenon of both HBsAg and antiHBs positive could not be attributed to mutation in HBV genome.