Fourteen species of bacteria were isolated from diseased grass-carps, Ctencpharyngodon idellus. Afer identification and inoculation tests, one of these bacteria (A-2), Aeromonas punctota Zimmermann, was found to be a pathogen for the grass carp. Aeromonas punctata is a gram negative, rod-shaped bacteria, motile by means of a single polar flagellum. It is able to digest gelatin, casein and starch, and gives positive reactions for catalase, indole, hydrogen sulfide, methyl red and acctylmethylcarbinol tests. It ferments most carbohydrates with the production of acid and gas.