The antigenic "a" determinant of the human hepatitis B virus surface antigen (HBsAg) is highly conserved and involved in inducing neutralizing antibody. Mutations on this determinant have been associated with the hepatitis B virus (HBV) escape from vaccination but are also found in chronic HBV carriers, but their involvement in liver diseases including hepatocellular carcinoma (HCC) is unclear. To investigate the possible liver disease-associated role of HBsAg mutants, their incidence was analyzed in 11 paraffin embedded HCC tissues using an improved DNA extraction method. Mutations on the "a" determinant (Thr126Ser, Gly145Arg, a double mutant Thr126Ser/Gln129Asn, Met 133Leu and Thr140Ile) were identified in 5 samples while the wild type sequence was found in 2 others. Future characterization of these HCC-associated HBsAg mutants should provide new insights on their role in the pathogenesis of HCC.