Abstract: Abstract:【Objective】To clone the NS1 gene of swine H9N2 subtype influenza A virus,and produce NS1 protein .【Method】The NS1 gene was amplified by RT-PCR, and then cloned into prokaryotic expression vector pET-28a(+).The recombinant plasmid pET-NS1 was extracted after being transformed into E.coli BL21-DE3 competent cells.【Result】 Restriction enzymes digestion and sequences analysis demonstrate that the recombinant plasmid carrying NS1 was inserted into correct open reading frame. The recombinant protein of NS1 about 26kD was produced after induction with 5 mmol/L lactose.The western-blotting test showed that the recombinant protein reacted with positive sera from pigs, not with negative sera. The OD650 value differences is distinctly that the positive sera 1280 fold dilution is about 3 times of the negative sera. 【Conclusion】These results lay the foundation of developing effective diagnostic method. Key words: Influenza virus; NS1; Antigenicity