Abstract: ObjectiveTo detect hepatitis B virus (HBV) genotypes and the effect of lamivudine on HBV mutations. MethodsRestriction sites and special primers for determination of HBV mutations and HBV genotypes were designed. HBV mutations and genotypes were determined by using RFLP. ResultsIn the 115 samples, 75(65%) were YMDD, 18(15.7%) were YIDD, 10(8.7%) were YVDD, 6 (5.2%)were YIDD+YVDD, 4(3.5%) were YMDD+YIDD and 2 (1.7%) were YMDD+YVDD; none were YSDD. At codon 180, 98 samples were wild types, 5(4.3%) were rtL180M，8(6.96%) were L180M+M204I, and 4（4.3%）were L180M+M204V. In 115 samples, 102 samples were genotype C and 13 samples were genotype B. The results of χ² test showed that the rate of lamivudine resistant mutations might not have a positive correlation with gender, HBV DNA levels and genotype (P＞0.05), however, they might have a positive correlation with time of lamivudine therapy （P＜0.05）, and the rate of lamivudine resistant mutations increased with prolonged lamivudine therapy. Also, mutation at codon 180 might have a positive correlation with that at codon 204 after lamivudine therapy（P＜0.05）. ConclusionYMDD mutations of HBV and genotype can be effectively determined by RFLP.

Key words: Hepatitis B viruses, Mutation, Genotype, YMDD, Restriction fragment length polymorphism