Direct Sky Blue-5B is an Azo dye known as general for staining of textile and leather, etc., and as materials which are difficult to be biodegraded in nature. The bacterium strain which could degrade direct Sky Blue-5B was isolated from activated sludge of dyeing factory and identified as Proteus sp. by experiment on morphological, cultural and biochemical characteristics, and so named Proteus sp. ST-1. The optimum condition of the strain for degradation of Sky Blue-5B were at about 35$^{circ}C$ and PH 7~8. The strain had been capable of degradation with organic nitrogen effectively and had completely degraded 200mg/1 of the dye within 12hrs at 37$^{circ}C$. The enzyme system related to degradation of Azo dye may be intracellular, and so degraded the dye after absorption into cell. The degradation products of Sky Blue-5B by Proton sp. 57-1 were analyzed by Gas Chromatography /Mass Spectrometry and Spectrophotomer, from this observation, it may be infered that the strain degraded the dye directly without any mediate.