To study the molecular-epidemiologic features of HIV1 epidemic strains from intravenous drug users (IVDUs) in Yunnan, nested primers polymerase chain reaction was developed for the amplification of env gene V3 fragment of HIV1 strains. DNA sequencing and analysis were performed with these fragments. Results showed that the variation of HIV1 gp120 V3 amino acids sequences among 16 HIV1, strains was averaged 7% (0%-23%), when comparing their consensus sequence. The amino acids consensus sequences of gp120 V3 region showed that more than 90% of homology compared with that of HIV1 SF2 strain and HIV1 American-European strain. However, lower homology with that of HIV1 strains from Haiti, Japan and Africa was revealed. The results suggested that there was a close relation among these 16 HIV1 epidemic strains isolated in Yunnan Ruili in terms of virus evolution. The epidemic HIV1 strains in the area were predominately American-European, SF2 and their derivatives in this period.