Abstract: Vibrio alginolyticus is an opportunist pathogen，which exists extensively in seawater，and causes diarrhea in humanand vibriosis in maricultured animals. Fewer studies on the extracellular product(ECP) of V. alginolyticus were reported. In our experiments the ECP was extracted from V. alginolyticus and the biological and physicochemical characters of the ECP were as-sessed. After V. alginolyticus had grown on tryptic soy agar(TSA) supplemented with 2％NaCl for 48h，the bacteria on the Petri dish were washed away by PBS，and the bacteria suspension was centrifuged at 10000 r/ min at 4 0C, then the supernatant was filtered through 0. 22μmfilter to obtain the extracellular products(ECP).The results showed that the ECP of V. alginolytics has amylase，casease，lecithinase and lipase activities，which the amylase activity was highest，casease and lipase activities sec-ondly，and lecithinase lowest，but has no gelatinase and urase activities. The ECP could dissolve the erythrocytes of lined silver grouper(Pomadasys hasta)，red drum(Sciaenops ocellatus) and redspotted grouper(Epinephelus akaara)，but not the ery-throcytes of chicken，sheep and o-type blood human. The LD50 value of ECP on mice and E. akaara were 0. 08 mg/ g and 0. 17mg/ g respectively，the 95%credibility ranges were 0. 06 -12mg/ g and 0. 07-28mg/ g respectively. 50mmol/ L ethylene-diamine tetra-acetie acid(FDTA) and 100mmol/L phenylmethylsulfonyl fluoride(PMSF) could reduce extracellular proteinase(ECPase) activities of V. alginolyticus by 83. 40%and 51.32%separately. The ECPase activities gradually rose with the in-crease of temperature from 4 ℃ to 50℃，and highest at 50 ℃，then dropped suddenly. The ECPase activities were gradually raided also with the enhancement of pH value，and highest at pH8.0，moreover higher at pH10. 6. Thus the ECPase has bad ther-monstability，and the optimal temperature and pH value of the ECPase is 50℃ and pH8.0 respectively.