Cell number of Vibrio spp. was examined for the surface and bottom sea water harvested from the 9 stations in the Jeonam Archipelago Marine Ranching Ground in 2006～2007. Species population composition and dominant species were analyzed as well. The largest number of Vibrio spp. was detected in summer (June, 2007) among the 4 seasons with the surface and bottom sea water samples of 5.4～93.2 cfu㎖-1 and 1.0～53.1 cfu㎖-1. respectively. In winter (January, 2007), Vibrio spp. was not detected at all except that one station from which 0.2 cfu㎖-1 of Vibrio spp. was counted in the surface sea water sample. Cell numbers were 0～11.9 cfu㎖-1 and 0～8.3 cfu㎖-1, respectively, in the surface and bottom sea water samples retrieved in spring (April, 2007), and the corresponding sea water samples in autumn(November, 2006) were contaminated with 0.1～21.4 cfu㎖-1 and 0～2.9 cfu㎖-1, respectively. Species population composition of Vibrio spp. was found to be V. parahaemolyticus, V. alginolyticus and V. cholerae non-01 among which V. parahaemolyticus and V. alginolyticus were dominant in all seasons. V. alginolyticus was detected from all stations even in the winter season indicating that this species seems to be less temperature dependent than the other Vibrio spp..