Abstract: Objective To explore the mechanism that how chymase affected diabetic cardiomyopathy by investigating the gene expression of chymase and the relationship between the gene expression of chymase and the angiotensin II in the cardiomyopathy of streptozotocin-induced diabetic hamasters. Methods Diabetic hamsters was induced by intraperitoneal injection of STZ 40mg/kg once a day for 3 days. After stabilization of diabetic state for 18 weeks, the myocardial ultrastructure was observed with electron microscope and pathologic changes were observed by microscope. Immunohistochemistry was used to measure the levels of expression of type I and type III collagen in diabetic and normal hamster hearts. Level of blood glucose, lipoprotein was determined using biocehemical methods. Apoptosis of cardiomyocyte was measured using TUNEL methods. Radioimmunuoassay method was used to determine the level of angiotensin II. RT-PCR was used to determine chymase gene expression (corrected byβ-actin). Results Comparing with the control group, levels of serum glucose, TG, TC, LDL in DM group were much higher. Concentrations of collagen I, III and angiotensin II ( 95.8±16.0 pg/mg tissue vs 51.1±20.8 pg/mg tissue) in myocardial tissue in DM group were much higher than those in control group. RT-PCR result showed: Comparing with the control group, the mRNA expression of chymase in DM group was promoted significantly (0.810±0.026 vs 0.490±0.087). Conclusion In diabetic hamsters, the gene expression of chymase were much higher than the control group, accompanying higher level of Angiotensin II, higher levels of expression of collagen I and III. This suggests that chymase plays an important role in the diabetic cardiomyopathy by promoting the activity of chymase.