Abstract: An epizootic outbroke in August, 1987, in adult rainbow trout reared in freshwater at Shuo County, Shanxi Province, was studied. Accordng to the virulence tests and the biochemical characteristics of the bacterial isolates, the parthogens were assigned to Aeromonas punctata. The hemolytic activity, caseinase and the lethal activity for fish of the ECP of the isolates were measured. Observation was also made on the histopathological signs produced by the ECP.