Abstract: The activity of lipoxygenase from rat liver cytosol to co-oxidase 8 chemicals were compared with that of the enzyme from rat lung.The optimum reactive conditions were pH 7.2 in Tris buffer, 3.5 mmol linoleic acid/L and 213 mg cytosolic protein/L for the liver enzyme, and pH 6.5 in Tris buffer,13.5 mmol linoleic acid/L and 213 mg cytosolic protein/L for the lung enzyme.Benzidine co-oxidation by the enzymes from liver and lung was obviously inhibated by nordihydroquaiaretic acid (NDGA) in a concentration-dependent manner.Besides benzidine,tetramethylbenzidine, guaiacal, pyrogallol,tetramythyl-p-pheny lenediamine,azinobis (3-ethybenzothiazoline-6-sulfonic acid,o-dianisidine and p-phenylenediamine also co-oxidated by the enzymes. Bot the metabolic activity of liver enzyme was only equitvalent to 12%～19% of lung's.The reasons for the difference may be:1. there are different lipoxygenase isozymes in liver and lung 2.the ratio and the amounl of liver enzyme in cytosolic protein are lower than that of lung enzyme. The results suggest that both lipoxygenases from liver and lune are involved in the oxidative processes of some chemicals that possess benzene ring structure and the enzymetic system is a important pathway of chemical metabolism in organisms.