To obtain fundamental data to prevent the disease of sea urchins Strongylocentrotus intermedius occurring at low water temperatures, an ecological survey on the causative bacterium, Vibrio sp. was carried out for one year at monthly intervals in 1996 at Date City Fisheries Breeding Center. The causative bacterium of the disease was detected in samples of seawater, on the surface of sea urchins and on rearing cages throughout the year. It was presumed that sea urchins suffered from injury or breakdown when they were gathered for handling of selection for shipping and consequently the disease occurred through invasion of the causative Vibrio into the coelome. To prevent this disease, effects of treatments with higher temperature, disinfectants, drugs and ultraviolet irradiation were examined by using two representative causative Vibrio strains Da-2 and Sr-3. Pathogenicity in experimental infection of both strains at 20℃ were similar to those at 11℃. They showed high sensitivity to benzyl penicillin and erythromycin, but were resistant to cloxacillin, spiramycin and chemotherapeutics. Their susceptibilities to ultraviolet irradiation were higher than that of causative bacterium Flexibacter sp. of spotting disease. Moreover, among the eight disinfectants tested in vitro, treatment with a 500 ppm chlorine dioxide for 30 min at 15°C was found to significantly disinfect the bacteria without any injury to the sea urchins.