Abstract: Vibrio alginolyticus is one of the most important opportunist pathogen,which exists extensively in seawater,and causes diarrhea in human and vibriosis in maricultured animals.The pathogenesis of V.alginolyticus disease is not clearly understood.In this article,the expression of some factors by V.alginolyticus HY9901 strain cultured in 15℃,20℃,28℃ and 37℃ was analyzed,respectively.The effects of culture temperature on bacterial growth were studied on TSA media.Poteolytic activity of Extracelluar protease(ECPase)were detected by the method of Azocasein.Virulence of extracelluar product(ECP)were studied by using Lethality for mice and Lutjanus sanguineus Cuvier.The results indicated that bacterial growth,poteolytic activity of Extracelluar protease(ECPase) and virulence of ECP all enhanced firstly and then dropped as the temperature rising,and 28℃ was the optimum temperature.ECP and outer membrane protein(OMP) expression were studied by using sodium dodecyl sulphate-polyacrylamide gel electrophoresis(SDS-PAGE).It was suggested that the bacteria showed diverse ECP and OMP profiles under different cultural temperatures.The major bands of ECP for V.alginolyticus was 70kD when the cells grown at 20℃,while 62kD ECP at 28℃.45kD OMP became denser when the cells grown temperature was rising,while 40kD and 34kD OMP became slight.The result also showed that SDS-PAGE purified ECP 62kD had strong poteolytic activity and Lethality for animals,and SDS-PAGE purified ECP 70kD had weak poteolytic activity and Lethality for animals.These results suggested that a virulent factor of V.alginolyticus may be induced or enhanced under 28℃.The temperature-regulated factors reported in this paper may be important in the pathogenesis of V.alginolyticus disease.The presented evidence also suggested that V.alginolyticus and possibly other bacteria destined for vaccine use in poikilothermic organisms should be cultured at temperatures consistent with that at which disease occurs.