This study examined the effects of the daily administration of high-molecular-weight (HMW) chitosan in drinking water (0.8 %) on kidney function in streptozotocin (STZ)-induced diabetic ICR mice. The HMW chitosan lowered the blood urea nitrogen (BUN), serum and urine creatinine levels, urine protein levels, and albuminuria and reduced the kidney weight in STZ-induced type 1 diabetic ICR mice. On histopathological findings, capillary loops are open, but narrowed, and the mesangial matrix enlarged in the STZ-induced diabetic ICR mice. By contrast, the capillary loops and mesangial matrix of the chitosan-treated ICR mice were nearly normal compared with the STZ-induced diabetic ICR mice.