Abstract: Objective To get recombinant Caf1M protein (rCaf1M) being of immunological activity, and construct assistant diagnosis of plague antibody. Methods The caf1M gene with removed signal peptide gene was connected with plasmid pGEX4t-1 by double-digested sites of NcoⅠ and XhoⅠ. Recombinant plasmid caf1M-pGEX4t-1was transformed into E.coli BL21 (DE3) and induced to express rCaf1M. Expression products of rCaf1M were purified by affinity chromatography. The dual detection NC film of plague antibody was constructed with purified rCaf1M and natural F1. Six sera which were F1 antibody positive and negative respectively of Zhejiang province were tested with above NC film. Results 55103 rCaf1M fusion protein was expressed by BL21strains containing caf1M-pGEX4t-1. The rCaf1M could react with plague anti-sera from rabbit and human. All 6 F1 antibody positive sera of Zhejiang province could react clearly with rCaf1M, whereas another 6 F1 antibody negative sera couldnt. Conclusion The rCaf1M developed by this study is of good immunoreactivity with plague anti-serum, and it can be used to serological ussistant examination of plague.