Thzring September 1989,an epizootic disease occured in shrimpfarms of Shangma Town, Laashan,Shandang province. The disease was describedas red leg disease,eharacterized by an egpansiou of chromatophores on the pereio-pods and pleopods, giving these appendages a reddish coloration, yBllow pigmentartion on the bronchial region of cephalathorag and swimming activity reducing. Theenrol)nph drew from moribund shrimp was thin, turbid and unclattablewastrains ef bacteria were isolated from hemalymph of moribund shrimps. Challengeexperiments showed that these isolates were some of the pathogens of the disease.The isolates were tested for 63 unit characters and classified as Protaus uugarzsHauler. The bacteria were Gram negative short rods with peritrichous flagella.Organic growth factors required. Swarming growth developed on the surface ofsolid media, Growth occued at 4℃to 42℃, and in 0%to 10%(w/v)sodium chla-ride, Catalase, indole,H₂S and phenylalanine deaminase were pxoduced. Oidase,β-galaetoaidase, arginine dihydrolase, lysine and ornithine decarboaylase werenot produeed,A positive result was recorded far methyl red test but not for VogesProakauer reaction, Gelatin and lecithin were degraded,Nitrate was reduced, Thebacteria produced gas from glucose, and said from glucose, sucrose and salicin,but not from arabinoae, cellobiose, mannitol, mannose, lactose, raffinose sndrhamnose. P. uLyar%s was first reported as the cauaitive agent of shrimp disease,