Abstract: ObjectiveTo analyze the characteristics of HA1 gene of influenza B virus isolated in Jilin province from 2005 to 2007, and to reveal the relationship between the influenza epidemic and the variation of HA1 region of the virus. MethodsInfluenza B virus was isolated and cultured by MDCK cell, the RNA was extracted and the HA1 gene was amplified by reverse transcription polymerase chain reaction (RT-PCR). The purified PCR products were sequenced. ResultsThe B/Yamagata lineage and B/Victoria lineage viruses co-circulated during 2005-2007. Compared with B/Shanghai/361/2002, B/Yamagata lineage virus circulated in Jilin in 2005 had 8 variant amino acids sites, B/Yamagata lineage virus circulated in 2007 had 10 variant amino acids sites. Compared with B/Malaysia/2506/04, B/Victoria lineage virus circulated in 2007 had only 3 variant amino acids sites. ConclusionCompared with B/Shanghai/361/2002, B/Yamagata lineage virus circulated in Jilin from 2005 to 2007 showed antigenic drift in HAI region; B/Victoria lineage virus was similar to the vaccine strain of B/Malaysia/2506/04.