Outer membrane protein (OMP) from Pasteurella multocida serotype B:2 was extracted and characterized using SDS-PAGE. Ten major polypeptide bands of MW 88 to 25 kDa were observed. Immunoblotting suggested that the polypeptides of MW 44, 37 and 30 kDa were the major immunogens. Buffalo calves vaccinated with the OMP vaccine or a commercial haemorrhagic septicaemia oil adjuvant vaccine developed highest mean log10 ELISA titres day 21 postvaccination (pv). Antibody titres detectable in these animals using an indirect haemagglutination assay were lower than the ELISA titres but the pattern of the antibody response was similar. A passive mouse protection assay revealed that the maximum protection against the challenge infection was conferred by the serum collected from both the groups on day 21 pv and 26 pv. Following challenge with virulent P. multocida cells, all the five OMP vaccinated animals survived whereas only 2 out of the 3 HS oil adjuvant vaccinated animals withstood the challenge. Results suggested that OMP was protective and could be used in vaccines against haemorrhagic septicaemia.