Bdellovibrios are obligate predatory bacteria, widely distribute in nature and regulate the counts of bacterium in water. Fifteen strains of predatory bacteria were isolated from marine environment using Vibrio parahaemolyticus DX-1 as host and one of them formed large plaques designated as Bd-M1. The strain was confirmed by Bdellovibrio species-specific 16S rDNA fragment amplified using PCR method. Determination of host range on species of fish pathogenic bacteria (Vibrio parahaemolyticus, Vibrio alginolyticus, Vibrio anguillarum, Vibrio anguillarum, Vibrio vulnificus and Edwardsiella tarta) indicated that Bd-M1 was able to parasitize 20 strains out of a total of 22 tested. Co-culture experiment shown that Bd-M1 have purification function on Vibrio parahaemolyticus, the number of V. parahaemolyticus decreased from 3.0′108 CFU/mL to 8.7×103 CFU/mL during 102 h. Immersion Penaeus vannamei in water at different concentration of Bd-M1 was used in protection against experimental infection with V. parahaemolyticus DX-1 infection. Results shown that the mortality of groups bathed with Bd-M1 was lower than that group without Bd-M1. These results suggest that it may be possible to use bdellovibrio to control fish disease.