A total of 84 Y. pseudotuberculosis isolates were studied. The isolates were obtained in Russian Federation in 1967-2008. The majority of Y. pseudotuberculosis isolates (n = 55) were of clinical origin and were isolated from feces of patients with the clinically and serologically proved diagnosis of pseudotuberculosis/Far East scarlet-like fever. These isolates included 18 isolates obtained from 3 outbreaks. Nine isolates were isolated from the internal organs of wild rodents. Other isolates were obtained from environmental sources. Ten Y. pseudotuberculosis isolates belonged to the serovar III and the other isolates belonged to the serovar I. The sequences of 600 b.p. fragment of the inv gene that encodes 667 through 866 invasin amino acids were determined for all isolates. Totally, 3 allelic variants were found. The most abundant allele 1 was found in 76 isolates. The allele 1 is represented in the database Genbank by the strain IP31758 isolated in the Far East of Russia (Eppinger et al., 2007). The allele 2 differed from allele 1 in 3 positions: G,2299N, O2300N, and O2302N. Substitutions in positions 2299 and 2302 were non-synonymous and resulted in amino acid substitutions Ser768 Thr and Val769 Ala. Six isolates carried allele 2. Allele 3 was found in two isolates different from allele 2 by a synonymous substitution G2324O. This allele is similar to the sequence found in Y. pestis strains, represented in the GenBank. The allelic distribution was not serovar specific: Y. pseudotuberculosis of serovar III and majority of serovar I isolates carried allele 1. The analysis of the allelic distribution among subpopulations formed on the base of a source of isolation revealed a statistically significant difference in spreading of alleles among clinical and wild rodent isolates (p < 0.05). Allele 1 prevailed over clinical isolates (95%), while allele 1 and allele 2 were disseminated equally among rodent isolates (55 % and 45 %, respectively).