Some Chronic HBV Carriers have persistent HBV replication despite the presence of anti-HBe Ag antibodies. This atypical chronic HBV infection has recently been related to the presence, in the pre-core region of HBV genome, of a translational stop codon that prevents HBeAg synthesis. We analyzed nucleotide sequences of the pre-core region of HBV isolated from the serum of an anti-HBe, HBV DNA positive severe chronic active hepatitis patient. Nucleotide sequence revealed that there was a point mutation from G to A at nucleotide 1896 of the pre-core region, converting tryptophan (TGG) to a stop codon (TAG). Additional mutation of A-T substitution at position 1846 was found. In conclusion, mutant HBV is responsible for developing severe anti-HBe positive chronic hepatitis B in Korea.