To obtain a recombinant influenza antigen,the HA gene of H1N1 subtype swine influenza virus(SIV) isolated from Guangdong Province was successfully amplified by RT-PCR and the sequence has been submitted in GenBank.The result showed that the HA gene of this SIV isolate is most closely related to that of SIV strains isolated in China mainland,Hongkong and the United States(with homology rate more than 89%).The PCR product was then cloned into pET-32a( ) to generate a prokaryotic recombinant plasmid pET32a-H1.After induced with IPTG,the HA gene was successfully expressed in the E.coli BL21(DE3).The highest expression content of the target protein added up to 25.2% of the total bacterial protein.Western-blotting analysis revealed that the recombinant protein could be recognized by H1N1 subtype SIV positive serum.