Abstract: This paper describes an epizootic septicemia of Penaeus chinensisinfected by Aero-moms hydrophila and A. caviae. The bacteria were gram negative,short rods with a single polar flagellum，resistant to O/129，no salt requirement,not growth on TCBS,ogidase and catalase positive. Gas was produced from fructose,mannitol,galactose and melibiose, but not from sucrose, maltose and starch. Thebacteria did not ferment lactose,inositol,sorbitol，aylose and trehalose dighdrate,arginine dighdrolase and tryptophan deaminase positive. Production gas fromglucose,V-P reaction,citrate utilization and sulfide production were all positive forA.hydrophila but not for A. caviae.