Objective To investigate the protective effect of catalpol on kidney and the expression of S100A8, TLR4 and NF-κB in diabetic rats. Methods Healthy male sprague-dawley rats were randomly divided into 3 groups: the normal control group, the diabetes model group, and the catalpol intervention group. The diabetic rats were induced by intraperitoneal injection with streptozotocin. The levels of fasting glucose, serum creatinine and urinary protein in each group were detected. The expression of S100A8, TLR4 and NF-κB in kidney were assessed by immunohistochemistry. The morphological changes of renal tissue were checked through microscopy. Results Compared with the model group, the levels of fasting blood glucose, serum creatinine and urinary protein in catalpol group were significantly decreased, and the expression levels of S100A8, TLR4 and NF-κB in renal cortex were dramatically decreased. Conclusion Catalpol has a protective effect on STZ induced diabetic rats, and its mechanism may be related to the decrease of fasting blood glucose level and the down regulation of S100A8, TLR4 and NF-κB protein expression in renal tissue.