Abstract: Objective To optin ize reaction conditions of repetitive extragenic palindrom is PCR (REP-PCR) finger printmap classification for Staphylococcus aureus and to apply the method in the classification of S.aureus clinic isolates and supply data for S.aureus homology tracing.Methods Cenom is DNA of S.aureus reference strain ATCC 25923 was abstracted with bacteria DNA abstract kit and used as the template for PCR.Target sequences in S.aureus genom is DNA were amplified with thepriners designed according to the reference.To obtain optin umfinger print maps,template,Mg²⁺，and priner concentrations of the reaction system and annealing temperature of PCR were optin ized Then 10 clinic strains of S.aureus were classified by optinum PCR.Results The electrophoresis bands of amplified products were most clear when 25μL of the reaction system contained 125 ng template,215 mmol/L Mg²⁺,0.6μmol/L each primer,and primers were annealed at 40℃.Each fingerprint maps of tenstrains of clinic isolates showed a band between 0.5 kb to 1.0 kb.The fingerprint maps of number 1,2,3,4,5,8,and 9 strain were same,and the maps of number 7 and 10 s train were also same.The fingerprint map of number 7 and 10 strain showed 3 bands,one in 5.0 kb-1.0 kb,one in 1.0-1.5 kb and one in 1.5-2.0 kb.The fingerprint map of number 6 strain showed 4 bands,of which two laid between 015 kb and 110 kb,one laid between 1.0 kb and 1.5 kb and one between 1.5 kb and 2.0 kb.Conclusion The optimum REP2PCR fingerprint map classification method of S.aureus was obtained and tenclinic strains of S.aureus were classified in to 3 types by the classification method.