Objective To study the origin of HIV-1 strains from 2 mother-to-child cases. Method DNA fragments of HIV-1 gag gene were amplified by nested PCR from the 4 target persons, and the amplified region were sequenced. Results The sequence of the specified fragment from all persons were analyzed and the strains were belonged to subtype A/E, while the sequence between mother's and child's is highly homologous. Conclusion 2 children were infected by mother-to-child transmission.