The paper concerns molecular study on pathogenicity markers of fourteen Y. enterocolitica O:9 isolated from pigs in which initially positive serological reactions for brucellosis were observed (n = 41), healthy pigs, which were brucellosis-negative (n = 258), and wild boars serologically negative for brucellosis (n = 209). PCR identification proved that all isolates were ail, ystA- and myfA-positive. The plasmid encoding yadA marker was detected in nine isolates that originated from pigs serologically positive or negative for brucellosis, and from one isolate of wild boar origin. Furthermore, none of the examined isolates was ystB-positive. Results of the investigations indicate that the Y. enterocolitica O:9 isolates from pigs or wild boars, regardless of whether they were serologically positive or negative for brucellosis, may also be potentially pathogenic for humans, due to the presence of chromosomal and plasmid encoded molecular markers.