Caulerpa lentillifera is a kind of edible seaweed, known as 'sea grape' or 'green caviar'. It is used in fresh salads. However, it is sensitive to low temperature and osmotic pressure, and is easily spoilt by storage in a refrigerator or washing with tap water. That is the reason why it is difficult to prevent food poisoning, especially due to Vibrio parahaemolyticus. In this study we investigated of marine bacteria and V. parahaemolyticus in C. lentillifera and cultured them in order to develop effective control of bacteria in commercial farms. The sixteen farms in the Okinawa Islands were investigated from August to September in 2006. A total of 176 samples were collected from eleven points during the cultivation processes and from the products. About 10(3) cfu/mL of marine bacteria were detected in the seawater used in the tank culture, but after cultivation of C. lentillifera the number had increased to about 10(6) cfu/mL. The number of marine bacteria in C. lentillifera did not change significantly through the process of planting to the final product (about 10(7) cfu/g). V. parahaemolyticus was detected in seawater from all processes and C. lentillifera was isolated from 56% of seawater, 25% of seed-stocks, and 18.8% of product samples, though but thermostable direct hemolysin gene was not detected from enrichment cultures or isolated V. parahaemolyticus strains. These results indicate that for prevention of food poisoning by V. parahaemolyticus in C. lentillifera, it is important to establish a suitable sterilization procedure for each process.