Removal of quinoline, which is typical of nitrogen-containing compounds in crude oil, was achieved by a biodegradation reaction by Comamonas sp TKV3-2-1. The aerobic strain, Comamonas sp TKV3-2-1, which can grow utilizing quinoline as the sources of both carbon and nitrogen, degraded quinoline to 2-hydroxyquinoline, finally to water-soluble substances. The degradation reaction of 2-hydroxyquinoline was revealed to be regarded as a rate-limiting step controlling the overall reaction of biodenitrogenation process of quinoline in crude oil. The degradation rate of 2-hydroxyquinoline in a stirred fermenter had a maximum of 211 mg 2-hydroxyquinoline g-cell-lh-l when the portion of crude oil in the reaction mixture, the cell concentration and the rotational speed of agitation impeller were 83.3%(v/v), 28.5 gdm(-3) and 11.7 s(-1), respectively. After the reaction was completed, the crude oil and the cell suspension could be separated efficiently by centrifuging. The possibility of constructing a bioprocess for removing quinoline in crude oil under storage is also discussed.