The complete (encoding 119 aminon acids, aa) or partial (encoding the N-terminal 90 aa) preS 1 region gene of hepatitis B virus (HBV) was fused to the 3’-end of glutathione-S-transferase (GST) gene and expressed at 37 degrees C under the control of the inducible tac promoter in E, coli. The results showed that the fusion protein with the full length of preS 1 was moderately expressed, about 10% of total cellular proteins, while the protein with the partial preS 1 was highly expressed, about 33% of total cellular proteins but the half was degraded into the protein with about N-terminal 60 aa of preS 1. Accordingly, GST fusion protein containing the N-terminal 56 aa of the preS 1, which still encodes B-and T-cell epitopes and a hepatocyte receptor binding site, was expressed under the same induction conditions and was shown to be highly and stably expressed, about 37% of total cellular proteins. The fusion protein with the full length or N-terminal 56 aa of preS 1 and the peptides were simply and successfully purified by affinity chromatography and were demonstrated to exhibit the antigenicity and immunogenicity of the preS 1 antigen.