[Objective] To investigate the effect of Xiao Si Wu Granules (XSWG), a preparation composed of Xiao Chaihu Decoction, Siwu Decoction and Witling Powder, on renal renin-angiotensin system (HAS) in diabetic rats. [Methods] Twenty-four Wistar rats were randomly divided into the normal, control and XSWG groups. Except the nonnal group, the rats in other groups were given one-dose intraperitoneal injection of streptozotocin (STZ) 65 mg/kg to induce diabetes mellitus (DM). After the establishment of diabetic models, XSWG group was treated with XSWG 1.8 g?kg-1?d-1 and the other two groups with the same dose of saline for 12 weeks. After treatment, the intrarenal angiotensin Ⅱ (Ang Ⅱ ) concentration was detected with radioimmunoassay method, renocortical antiotensin-converting enzyme (ACE) activity with ultraviolet spectrophotometry and renocortical angiotensin Ⅱ receptor type 1 (AT1) mRNA level with reverse transcriptase polymerase chain reaction (RT-PCR). [Results] AngⅡ concentration and renocortical ACE activity were increased, and renocortical AT1 mRNA level was decreased in the model group, the difference being significant as compared with the normal group ( P