Yersiniosis is ubiquitous and causes great damage and death. The genus Yersinia has 11 species, 3 of which are characteristic of human disease: Yersinia pestis, Yersinia enterocolitica and Yersinia pseudotuberculosis. Based on serotyping, this pathogen is classified into more than 57 serogroups. Pathogenic serotypes are O: 3 (biogroup 4), O: 5.27 (biogroup 2 and 3), O: 8 (biogroup 1B) and O: 9 (biogroup 2). The most common serogroups isolated from humans in European countries are O: 3 and then O: 9. In the United States, for example, the more common serogroup O: 8. In general, 11 serovars are most associated with human infections (O: 3, O: 4, O: 5.27, O: 8, O: 9, O: 13, O: 18, O: 20, O: 21). The publication presents data on the activity of two microseries of Yersinia Enterocolitica serovariants O3, O5, O6.30, O8, O9 by serological predictions in the samples of RA. In the process of obtaining and increasing the activity of two microseries of microseries, the methodology of obtaining components in a set, designated for serological diagnostics of tincture in the RA, was developed. The effectiveness of experimental samples of Yersinia sera was studied. Serum Yersinia enterocolitica O3 of microseries 1, O8 of microseries 2 and O9 of both microseries were determined to be highly specific. Yersinia sera of serovar O6.30 microseries 1, as well as O3, O5, O9 of both microseries are active in a titer of not less than 1: 400. It is established that according to this method of obtaining RA components allows to detect specific antibodies in the sera of animals in the titer of 1: 400–1: 800. Due to the antigenic affinity of strains of serotypes O5 and O6.30, there is a need to pay more attention to the selection of Yersinia, in particular to work with antigenically homogeneous clones, which will avoid nonspecific intraspecific cross-reactions, respectively, increase the specificity of sera.