A total of 150 sera samples from volunteers (30 belonging to each of the A, B, O blood group) with 120 of them without history of diarrhoea infection (asymptomatic) and 30 with diarrhoea (symptomatic) were collected using standard technique. Bactericidal activities of the sera were tested against local isolates of Yersinia pseudotuberculosis, Y. enterocolitica 0:3, Y. enterocolitica 0:8, Y. kristensenii 0:11, 23, Y. intermedia 0:52, 53 and Y. intermedia-like bacteria 0:52, 53, using micro titre plate technique. The Y. enterocolitica 0:3 (89.15%) was found to be the most sensitive to the bactericidal effect of sera of blood group A individuals, while Y. kristensenii 0:11, 23 (45.58%), was the least susceptible. For group B sera, Y. pseudotuberculosis was the most sensitive (97.26%), while Y. intermedia 0:52, 53 (48.26%) was the least sensitive. Yersinia enterocolitica 0:3 (90.04%) was the most sensitive to blood group AB sera, while Y. enterocolitica 0:8 (52.77%) was the least sensitive. For sera of blood group O, only Y. pseudotuberculosis (56.77%) and Y. enterocolitica 0:3 (64.85) were sensitive, while other Yersinia species were resistant. The results of this study suggest that individuals with blood group O whose sera caused a relatively lower bactericidal effect will be more susceptible to Yersiniosis than individuals with other blood groups (A, B and AB). The result further suggests that circulating antibodies and/or lymphocytes induced by diarrhoeic organisms could assist in the elimination of Yersinia species from the blood of individuals suffering from Yersinia bacteraemia, a finding which is of both epidemiological and clinical significance.