Abstract: The culture of red sea bream(Pagrus major) has undergone rapid development in recent years in China,however,suc- cessful production is increasingly hampered by diseases.Vibriosis,caused by Vibrio mimicus,has become a major cause of serious economical losses in the farming of red sea bream along the coast of southern China.Vm-Pm toxin was successfully purified from the culture supernatant of Vibrio mimicus strain 96-6-3,using sequential ammonium sulfate precipitation and column chromatogra-phy on DEAE-cellulose and Sephadex G100. In the present paper,the immunological characteristics of Vm-Pm toxin were stud-ied. Rabbits were immuned with three kinds of exotoxins to raise the anti-sera.After the exotoxins reacted with the anti-sera,their haemolytic and cytotoxic activities were examinated. The results showed that the Vm-Pm toxin was neutralized by anti-sera,then lost its haemolytic and cytotoxic activities.On the contrary,the HEC toxin and cholera enterotoxin still kept their haemolytic and cytotoxic activities after neutralization. Red sea breams (P. major)were injected intramuscularly and direct immersion withforma-linized Vm2Pm toxin(toxoid). The effectiveness of vaccination against V. mimicus was evaluated two weeks after the immuniza2 tion. The results showed that stronger protection was induced in red sea bream by toxoid.After booster immunization,this protec-tion was enhanced.