Cross-sectional study for determining the prevalence of Ovine pasturellosis, in-vivo evaluation of the level of protective antibody titer before and after vaccination against the disease and proofing the farmers and animal health experts complaint of its cause on small ruminant production despite annual vaccination program against the disease in Adiyo district of Boka-Shuta and Buta Kebelle, Kaffa Zone. The study was conducted from July 2012 to June 2013 and the study kebelles were purposively selected based on sheep production potential, the disease’s report and farmers’ complaint on the vaccine’s inefficacy for protecting the sheep against the disease. For these, the study was designed to answer the above stated objectives with two consecutive phases, viz. prevalence study followed by in-vivo antibody titer evaluation. For prevalence study, 192 blood samples were needed and calculated, but for more accuracy 200 samples were collected randomly from previously unvaccinated sheep population (in less than 1 year) against ovine pasturellosis disease. For in-vivo evaluation, 52 blood samples were randomly collected from selected sheep population after they were vaccinated against ovine pasturellosis disease with P. multocida biotype A-vaccine by grouping them based on history of vaccination status (not vaccinated in less than 1 year against ovine pasturellosis disease) and age group (greater than 6 months of age). Sample collection, preservation and transportation were performed according to the recommended standard procedures. Laboratory analysis, Indirect haemagglutination Inhibition Test was employed at National Veterinary Institute (NVI), Ethiopia for both studies. Thus, out of 200 serum samples, 175 (87.5%) were positive. However, there were no statistical significant difference (p ≥ 0.05) between study areas, age and sex of the animals. Regarding in-vivo evaluation of the level of protective antibody titer, it was found 87.5% before vaccination and 98,1% a