The 105 strains with high virulence of Yersinia pestis from 17 ecotype, 4 strains with low virulence, preserved by our laboratory, 6 Yersinia pseudotuberculosis strains, 4 Yersinia enterocolitica strains and 3 strains of the other intestinal canal bacteria were t[WT5,5”BZ]ested by Yop1 McAb RIHA. While the strains of Y.pseudotuberculosis and Y.enterocolitica appeared positive reaction (dilution rate:2 7~10 ),negative reaction were produced in the rest strains. These suggested:(1) Yop1 be the exclusive protein of Yersinia spp.; (2)The possibility of reverse mutation of yopA gene in Yersinia pestis be very little (the detailed research will report in another essay); (3)The Yop1 McAb and its immune measure techniques have more widespread prospects in the differential diagnosis between the Yersinia pestis[WT5,5”BZ] and Yersinia pseudotuberculosis [WT5,5”BZ]and between the Yersinia enterocolitica serotype O∶9 and Brucilla spp.