Abstract: "Rotten-Skin" disease is a bacterial ailment of the Chinese River Dolphin （Lipotes reexillifer） which was captured and reared in a concrete pond. As the name signifies, rotten skin is characterized by the formation symptomatic of necrosis on the surface of the body.The bacteria are short, straight, Gram-negative rods with rounded ends, measuring 0.4—0.5×0.7—2.2 microns. They occur singly or in pairs, and are actively motile by virtue of 3—5 polar flagella.Cultures are capable of producing a yellow-green diffusible fluorescent pigment on the King B medium. Stratiform liquefaction of gelatin appears in 24 hrs （20℃）. On the media cintaining 2—4% sucrose, colonies are slimy as a result of leven formation. Litmus milk cultures become alkaline, peptonized and become clear.Oxidative utilization on carbohydrates display in Hugh and Leifson's medium, e.g. pridueing weak acid but no gas. The same holds true in l-arabinose, xylose, galactose, lactose, salicin glycerol, mannitol, adonitol, inositol, sorbitol, cellobiose, and trehalose. Raffinose, sucrose, starch, propylene glycol, erythritol, dextrin, ethanol, aesculin, rham nose, dulcitol and glycogen are not utilized.The egg yolk, the oxidase reaction, saceharate, the arginine dihydrolase and the production of nitrites are positive. Tests with methyl-red and Voges-Proskauer reaction, and the formation of H2S, are all negative. There is no capacity to denitrify. The optimal temperature for growth appears to be between 20—30℃. The strain will not grow at 41℃, but can grow at 4℃. Growth is weak at 37℃.The healthy fishes were soaked or rubbed with 18-hr, culture, a symptom similar to that of the natural infection of the skin with Pseudomonas fluorecens was revealed. But the skin of white mice is unaffected by the bacteria. Although Lipotes is a homoiothermal animal, its skin is exposed to water, while the skin of white mice is in air and much warmer （37.5—38℃）.According to above mentioned characters it fits well to the characteristics of Pseudomonas fluorescens Migula 1895, which was presented in Bergey's Manul 8th edition by Stanier. We consider that Pseudomonas fluorescens biotype I （biotype A of Stanier et al., 1966） is likely the causative agent for the "Rotten-Skin" disease of Chinese River Dolphin.