Fifty-two pathogenic Vibrio parahaemolyticus strains were isolated from the environments of Busan and Yeosu, Korea. Forty-three of these strains showed protease activities, whereas 4 strains showed $alpha / eta$ hemolysin activities and 6 strains had urease activities. Their pathogenic factors were not overlapping except one strain, which had both protease and hemolysin activities. The 6 urease-positive strains (V. parahaemolyticus YKB4, YKB14, S25, YFB20, YFO21, and YFO22) showed the same biochemical characteristics as a reference strain [V. parahaemolyticus KCTC 2471 (urease-negative)], except for urease production. The 6 urease-positive strains showed different urease activities in their culture supernatant during the growth. The urease activity of S25 increased sharply at the late exponential phase, and was the highest at the initial stationary phase and was kept until the late stationary phase. The other 5 isolates, except C25, showed urease activities at the mid-stationary phase and increased steadily until the late stationary phase, when the urease activity was maximal. To compare the degree of virulence of V. parahaemolyticus with different pathogenic factors, hemolysin, protease, or urease-positive strains were injected into groups of 10 each of ICR mice (7- to l0-week-old males). The lethal rates of urease-positive V. parahaemolyticus, YKB14, YKB4, and S25, were significantly high, being 50, 70, and 80%, respectively. Protease-positive V. parahaemolyticus strains FM39 and FM50 showed 40% and 60% of lethal rate, respectively. Hemolysin-positive V. parahaemolyticus strains S34 and S72 had no mortality, similar to nonpathogenic V. parahaemolyticus FM12.