< p > Vibrio vulnificus isolated from diseased Mullet, Mugil cephalus L., were immunized with formalin inactivated Vibrio vulnificus to the juveniles of priming and booster groups of fish. Assessing the humoral immune response using the serum agglutination assays. This experiment was performed to compare the antibody titre in priming dose and booster dose. The result revealed that the higher priming response at 21 dpp and booster response at 35 dpb. This intramuscular injection was more suitable for inducing the primary response than intraperitoneal injection.