Abstract: The pathogenic strains B 1 and B2 were isolated from diseased Carassius auratus. And five strains of Bdellovibrio were isolated from the mud in the culture area of crab in Southern Four Lakes and Bdellovibrio BD04 was selected to study its biological characteristics preliminarily. The results showed that Bdellovibrio BD04 could not only lyse fish-pathogenic bacteria, but it could also lyse E. coli C600 and Staphylococcus aureus and other bacteria. And the optimum temperature was 30 ℃ and the optimum pH was 8.2. The research results demonstrated that BdeUovibrio as a kind of biological purification had greater developmental potential and application values.