Many herbal remedies individually or in combination have been recommended in various medical treatises for the cure of different diseases. In the search of natural hypoglycemic agents as alternatives to synthetic ones and to justify the use of Syzygium cumini seeds in folklore system of medicine for diabetes, the hypoglycemic and hypolipidernic activity of Syzygium cumini seeds were investigated in normal and non insulin dependent diabetes mellitus (NIDDM) rats. Diabetes was induced by streptozotocin in neonates. Administration of petroleum ether, chloroform, acetone, methanol and water extracts of Syzygium cumini seeds (100 mg/kg, p.o.) for 21 days caused a decrease in fasting blood sugar in diabetic rats (FBS). Among all the extracts methanol extract was found to lower the FBS significantly in diabetic rats. Glibenclamide at a dose of 5 mg/kg p.o was used for comparision. Methanol extract was subjected to column chromatography which led to the isolation of an active principle, which was given trivial name Cuminoside. Cuminoside (50 mg/kg, p.o.) caused significant reduction in fasting blood sugar in diabetic rats. Further it also caused a significant reduction in cholesterol, triglycerides, low density lipoprotein (LDL), hepatic enzymes such as aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH) level and improvement in the level of high density lipoproteins (HDL) in diabetic rats. Reduction in the fasting blood sugar, normalization of liver enzymes level and improvement in the lipid profile by Cuminoside indicates that Cuminoside has cardio protective potential with antidiabetic activity and provides a scientific rationale for the use of Cuminoside as an antidiabetic agent.