In order to clarify the role of peroxisomal fatty acid β-oxidation and D-bifunction protein (D-BP) in lipid metabolism disorder of diabetes mellitus(DM), the number of peroxisomes by electronic microscope and the activities of major enzymes involved in peroxisomal β-oxidation in livers from STZ-induced diabetic and normal rats are compared respectively. Catalase and D-BP protein level was determined by Western blot. In the livers of STZ-induced diabetic rats, the peroxisomes proliferated and showed some morphological changes, while the protein amount and activity of catalase significantly increased. Although the activities of acyl-CoA oxidase, L-3-hydroxyacyl-CoA dehydrogenase and fatty acid β-oxidation of peroxisome in the diabetic rat liver were significantly increased, the protein amount and activity of D-BP in the diabetic rat liver was decreased compared to control rats. The relationship between decreased D-BP activity and lipid metabolism disorder in DM was also discussed.