Abstract: A bacterial strain capable of utilizing quinoline as sole source of carbon, nitrogen and energy was isolated from the petroleum contaminated soil of a petrochemical refinery. The isolate was identified as Enterobacter sp. having strong quinoline degradability. Biodegradation experiments showed that this strain could degrade 486 mg/L of quinoline in pure culture completely within 30 h. Said bacteria not only could degrade quinoline with high concentration in refinery wastewater efficiently, but also could co-treat other organic pollutants together with other organisms to further reduce the CODCr of effluent. The activity of nitrobacterium was inhibited by the high concentration of quinoline temporarily, yet it could be recovered in about one week. The biodegradation of quinoline released as ammonia into the growth medium, which increased the load of ammonia, however, the decrease of ammonia removal rate was also temporary. The degradation of quinoline followed zero-order kinetics equation when the concentration of quinoline in the range of 200 to 686 mg/L.