To enhance the immunogenicity of hCGbeta protein vaccine and the hCG neutralization capacity of anti-serum by using the molecular adjuvant C3d3, the secreted 6his-hCGbeta-C3d3 fusion protein and 6his-hCGbeta were expressed in CHO cells and purified with Ni(2+)-chelating chromatography and Sephadex G-150 column. Then we investigated the potential of three copies of C3d as the molecular adjuvant of hCGbeta protein antigen. The antibody response to hCGbeta-C3d3 conjugates was compared with those resulting from immunization with hCGbeta alone and hCGbeta plus CFA/IFA in BALB/c mice. Our results showed that the antibody titer of hCGbeta-C3d3 was 1995-fold higher than that of hCGbeta alone and the anti-serum was capable effectively neutralizing the bioactivity of hCG. The immunity-enhancing action of C3d3 was 10-fold (primer) and 32-fold (booster) greater than CFA/IFA. These results indicated that C3d3 conjugates might be a better way to overcome the poor immunogenicity of hCGbeta contraceptive vaccine.