We examined a possible preventive effect of Linderae radix (LR), the root of Lindera strychnifolia, on the progression of diabetic nephropathy. Water extract of Linderae radix (LR extract) was orally administered to the C57BL/KsJ-db/db (db/db) mice, a model of genetic diabetes, at a dose of 730 mg/kg/day for 12 week. The LR extract treatment did not affect glucose metabolism and systolic pressure. However, it resulted in a better renal function as evaluated by creatinine clearance (Ccr) and serum creatinine than the control; Ccr and serum creatinine were progressively worsened in controls (0.13+/-0.01 (l/day) and 0.69+/-0.04 (mg/dl), respectively) whereas unchanged in the treated group (0.24+/-0.03 (l/day), p<0.05 and 0.53+/-0.04 (mg/dl), p<0.05, respectively). Kidneys of the LR extract-treated group showed glomeruli with greater area and cell population, smaller glomerular sclerotic index, and less fibrosis in glomeruli, where apoptotic rate of glomerular cells were decreased compared with the control kidneys. Furthermore, renal TGF-beta(1) expression was decreased in the LR extract-treated group. These findings suggest that the LR therapy can be a novel therapeutic approach against diabetic nephropathy.