Abstract: The ulcer disease of marine cage-cultured large yellow croakers, Pseudosciaena crocea (Richardson) in Zhejiang Province was investigated in this paper. A bacterial strains (824-1), isolated from diseased large yellow croakers, was proved to be the pathogenic bacterium by artificial infection experiments, and identified to be Vibrio alginolyticus by the morphological and cultural features, physiological and biochemical characteristics. The extracellular products of strain 824-1 were studied by cylinde-plate method. The results showed that the extracellular products included amylase, gelatinase, lipase, casease, haemolysin, lecithinase and chitinase, but didn′t contain urease. The sensitivity of the bacterial isolate to 35 antibacterial agents (20 chemotherapeutants and 15 Chinese herbal medicines) was evaluated. It revealed that 3 chemotherapeutants (Co. SMZ, Sulfarmehoxazole/Trimethoprim and Gentamycinum) and 4 Chinese herbal medicines (Pericarpium granati, Rhizoma sanguisorbae, Fructus schizandrae, Rheum officinale) were examined as the most effective antibacterial agents.