Abstract: ObjectiveTo understand amino acid sequences of RNA segment 4 for revealing the relationship of new avian influenza A(H9N2)vir uses.MethodsVirus RNA was transeribed into cDNA by reverse transcriptase,cDNA amplifed by PCR.The productions of PCR were puriffied.RNA sequence analysis was performed by the dideoxy nucleotide chain ter mination method using synthetic oligo deoxynucleotide primers.ResultsThe length of quHK 197,swHK 998,ckHK 997 and tywis66 H9N2 virus RNA segment 4 contains 1 672,1 670,1 651 and 1 683 nucleotides,respectively,encoding for HA(530561 amino acids)proteins.The homologies of amino acid sequences of HA proteins were in the range of 92.7% to 96.9% in this three virus,but were in the range of 87.8% to 89.0%.ConclusionThe homology of amino acid sequenes of HA proteins of new avian influenza A(H9N2)was different from tywis66 H9N2 virus.