Objective To establish an indirect immunofluorescent assay(IFA)of Y.pestis F1 antibody detection in rat serum with expressed F1 antigen.Methods pCDNA3.1-hisB-caf1 was reconstructed by gene clone and recombination techniques.The vector was then transfected into NH3T3 cells with lipofectamine.The positive cell clones were selected with G418.The cells stably expressing F1 antigen were used to detect F1 antibody in rat serum with IFA.Results The recombinant vector expressed the F1 protein stably in NH3T3 cells.The purified F1 protein could react specifically with rat serum,which was confirmed by ELISA.Conclusion The F1 protein expressed in NH3T3 cells could be a valuable candidate of antigen for detecting F1 antibody in rat.