A total of 52 pathogenic Vibrio strains was isolated from the Gwangan Beach during summer in 2003. The isolated vibrios were composed of 6 different species: V. parahaemolyticus, V. cholerae non O1, V. fluvialis, V. vulnificus, V. alginolyticus, and V. mimicus. V. parahaemolyticus was most predominant as $46\%$ (24/52), V. cholerae non O1 was the second with $23\%$ (12/52), and V. fluvialis was the third with $17\%$ (9/52). Among the isolated strains, 22 strains showed hemolytic, proteolytic or ureolytic activity. Eight strains showed both hemolysin and protease activities, and either 6 strains showed only hemolysin activities and 7 strains only protease activities. Only one strain of V. parahaemolyticus isolates showed urease activity. The urease-positive V. parahaemolyticus strain (V. parahaemolyticus S25) showed the same biochemical characteristics as the reference strain, V. parahaemolyticus KCTC 2471 (ureasenegative) except for urease production. To compare the degree of virulence of Vibrio strains having different pathogenic factors, hemolysin, protease, or urease-positive strains were injected into groups of 10 each of ICR mice (7- to l0-week-old male). The lethal rate of urease-positive V. parahaemolyticus S25 was significantly high, being $70\%$. Protease-positive strains showed $40-60\%$ of lethal rate. Hemolysin-positive strains showed no mortality, similar to non-pathogenic V. parahaemolyticus KCTC 2471 and V. parahaemolyticus FM12.
