Objective To investigate the variations of surface protein genes of avian influenza virus (AIV)before and after infecting mouse.Methods Mouse lung tissue was infected with A/Goose/Guangaong/NH/2003(H5N1)and the virus was isolated 12 hours and 9 days after replication in lung tissue of mouse.The isolated strains were amplified in embryonated chicken eggs,anti the virion RNA was transcribed into cDNA by reverse transeriptase.After amplification and purification,dideoxy-mediated chain termination was performed to detect synthetic oligonucleotide primers and DNA sequence was analyzed.Results The homology of nucleotide sequence for HA gene of three isolated strains was 99.6%-99.8%.and that of amino acid sequences was 99.3%-99.6%.The homology of nucleotide sequence for NA gene of three strains was 99.8%-99.9%.all of them were synonymous mutatinns.No variation was found in M gene.Conclusion After replication in mouse lung tissue,no significant mutation was found in the surface protein genes of AIV except some point mutations in HA genes.