Pasteurella multocida (P. multocida), A Gram-negative facultative anaerobic bacterium, is a causative animal pathogen in porcine atrophic rhinitis and avian fowl cholera. The outer membrane of Gram-negative bacteria contains of many different protein in very high copy numbers. One of the major outer membrane,
the H proteins have functional as high immunogenicity and antigenicity. In this study to increase information about epidemiology of ovine and bovine P. multocida, the 24 isolates from sheep and nine isolates from cattle were investigated by PCR-RFLP analysis of the ompH gene. In all 33 isolates, digestion
of the amplified fragment of ompH gene by using EcoRI, cfoI and HindIII produced 3, 5 and 3 different restriction patterns respectively. Sixteen RFLP patterns were found among 33 investigated P.multocida isolates. This study showed that, the PCR RFLP based on ompH gene is potentially a useful method for
typing of P. multocida isolates from sheep and cattle. The RFLP patterns of this gene exhibited extensive restriction site heterogeneity, which may be particularly suitable for fingerprinting of P. multocida isolates. Considering ompH protein as a protective immunogenic moiety of P. multocida, the results of this study
showed a heterogenic bacteria and this means the possibility to produce a multivalent vaccine to be protective against diseases caused by this organism in sheep and cattle in Iran.