The renal protective effect of an active principle isolated from the aqueous extract of fruit pulp of Eugenia jambolana was investigated in streptozotocin (45 mg/kg body weight)-induced severely diabetic rats (FBG > or = 300 mg/dl). For isolation of active principle, crude aqueous extract of E. jambolana fruit pulp was subjected to purification by ion-exchange column chromatography, which yielded a partially purified compound (FII), which on further purification by rechromatography gave a purified active compound (FIIc). Purity of FIIc was confirmed by high pressure liquid chromatography. Detailed UV, NMR, IR spectra suggested that FIIc is a small aliphatic organic compound having molecular formula C4H7O4N. Oral administration of FIIc to diabetic rats (10, 15 and 20 mg/kg body weight per day for a period of 60 days) produced significant (P<0.001) fall in fasting blood glucose (FBG) in a dose-dependent manner. Treatment with FIIc (15 mg/kg body wt.) showed significant (P<0.001) improvement in body weight, blood urea, plasma creatinine levels, urinary volume, urinary sugar and microalbuminuria. Renal hypertrophy, assessed as the ratio of the weight of the two kidneys to total body weight was also significantly (P<0.05) improved after treatment with FIIc. The above results suggest that FIIc possesses significant nephroprotective activity.