Forty buffaloes (group A) and 40 buffalo calves of either sex between 3 to 6 months age (groups Band C) were inoculated with oil adjuvant Haemorrhagic septicemia vaccine. The calves of group C were given a booster dose of vaccine after 90 days. The immunity conferred by oil adjuvant vaccine against Haemorrhagic septicaemia lasted for one year in adult buffaloes whereas, it lasted for seven months in calves. In calves which were injected booster dose, the immunity conferred persisted for more than one year.