OBJECTIVE To study the antigenic and genetic characteristics of influenza A (H3N2) virus in the 2009 influenza epidemics in Chengdu. METHODS The influenza virus strains were isolated with MDCK cells from 4869 samples taken from the sentinel surveillance in 2009 in Chengdu. Hemagglutination inhibition (HI) and RT-PCR reaction tests were performed to guide the extraction of viral RNA from the culture fluid of the influenza A (H3N2) virus. The hemagglutinin gene was obtained by RT-PCR and sequenced. RESULTS The separation rates of swine influenza H1N1, H3N2, H1N1, and B were 25.2%, 7.2%, 4.5%, and 1.5% respectively. The epidemic peaked in summer and autumn. Four amino acids changed in A, B, and D antigenic and receptor binding sites: site160N>K, site174K>R/N, site189K>Q, site277R>Q. Glycosylation sites were inserted to sitel60 or absent at site181 in some isolated strains. CONCLUSIONS Swine influenza H1N1 viruses dominated the 2009 Chengdu epidemic, with H3N2, H1N1, and B strains coexisting. The influenza A(H3N2) viruses had gene variations due to antigenic drift.