Abstract: The paper deals with, pathogenicity and pathological changes induced of the Chinese river crab caused by Citrobacter freudii, medicinal sensitive tests of the pathogen and therapeutic effect of medicine in production. The pathogen was separated from hepatopancreas of moribund and diseased crabs. It was proved that this bacteria had caused the health crab infected and death through artificial infecting tests and the mortality was 100%. The pathogen was identified as Citrobacter freudii by the biological and biochemical determination. The pathogen could induce pathological changes of hepatopancreas and gill of river crab, and finally the septemia and death. Effective medicine was screened through the medicinal sensitive tests to the pathogen of 16 kind of drugs, and curative effect was observed in production.