Aim To explore the relationship between cathepsin S in the process occurrence and development of atherosclerosis in diabetes. Methods 83 diabetic patients detected by carotid artery intima-media thickness(IMT) were divided into three groups: 20 diabetic cases with moderate atherosclerosis group,IMT≥1.0 mm,or with more than one atherosclerotic plaque;23 diabetic cases with mild atherosclerosis group,IMT 0.8~0.99 mm;40 diabetic cases without atherosclerosis group,IMT <0.8 mm;21 cases of normal control group.The levels of HbA1c,CatS,blood glucose,blood lipids,IMT results were measured in all subjects. Results Compared with the control group CatS value was significantly higher in diabetic group with moderate atherosclerosis and mild atherosclerosis(P><0.001),and increased positively with IMT;CatS value had no significant change in diabetic group without atherosclerosis and the normal control group(P><0.05);compared with the first group and the second group CatS value was significantly different(P><0.001);in the diabetic group of glucose,blood lipids,HbA1c was not significantly different(P><0.05),and in normal control group was significantly different(P><0.01). Conclusion CatS level in diabetic patients was significantly increased,and related to IMT values.CatS determination of serum can be used as diagnostic indicators for monitoring diabetes,atherosclerosis.