Abstract: Avian Pasteurella multocida strain C48-19(serotype1), P1059 (serotype3) grown in brain-heart infusion broth containing the iron chelator dipyridyl expressed additional outer membrane proteins (OMPs) compared with those grown in normal brain-heart infusion. These OMPs were merely expressed in iron deficient medium and were considered to be iron-regulated outer membrane proteins (IROMPs). The SDS-PAGE patterns showed the existence of 87, 81, 79, 64, 60.5 ku IROMPs in both strains. The following Western blotting demonstrated that 87, 79, 60.5 ku proteins can be recognized by the convalescent serum from chicken recovered form C48-19′s infection. These three proteins were considered to be conserved IROMPs with cross immunoreactivity, and might be common antigens of these two strains that expressed in vivo. Furthermore, OMPs of C48-19 grown in chicken allantolic fluid shared similar pattern with those grown in iron depleted media.