Objective：To investigate the changing trend of hepatitis B virus（HBV） “a” determinant quasispecies in 5 children who failed to responded to hepatitis B vaccine and their mothers. Methods：Five children who developed into chronic HBV infection after receiving hepatitis B vaccine and their respective mothers were enrolled into the research. The full HBV genome was amplified by polymerase chain reaction（PCR） and the sequences were determined by Solexa sequencing technology. Results：The sequence homology between paired mother and child was beyond 99%. The HBV genotype in 5 pairs of mother-child was mixture of B and C. Among them，4 pairs had dominant B while the other 1 pair had dominant C. The dominant HBV genotype was identical between paired mothers and children. Significant complexity positions could be found in every immunized child. There were 10 significant complexity positions in “a” determinant region in 5 pairs of mother-child；aa126 and aa143 were observed only in one child. And one child had G145R mutant. Conclusion：“a” determinant quasispecies can be found in children who failed to responded to hepatitis B vaccine. The mutant strain in child may be transferred from her mother.