||Studies on the efficacy of vaccines were conducted in the cobia using pathogenic Ph. damselae ssp. piscicida… ( strain 9304 ) and V. alginolylicus ( strain AL1) originally isolated from moribund cage-cultured cobia. Bacterial cells and ECPs were obtained by growing the bacteria, Phdp 9304 and Val AL1 on YFP broth (adding NaCl, O.Salts, dipyridyl and glucose) and BHIA-cellophane overlay agar (adding NaCl and dipyridyl), respectively. Bacterial cells and ECPs were inactivated by 1% and 3% formalin, respectively. All the three vaccine preparations were intraperitoneally(i.p.) injected into cobia ( 10g ) with 250 fish in each treatment. After vaccination, the fish were boostered orally for one week at week 4 and 8. Fish of each treatment were lethally challenged with respectiue bacteria. The results of 12-week vaccination trials revealed that better efficacies were obseyved in treatments with bacterial cell of V.al AL1 ( 96% survival rate), bacterial cells of Phdp 9304: FP group ( 96% survival rate) ,EP group ( 84% survival rate). The present results showed better protection than those of previous year. Therefore, the continuous isolation of more virulent bacteia and manipulation of growth media are crucial to the development of better vaccines.