A number of plants including Berberis aristata roots are considered effective as antidiabetic agents in ethnomedical practices. In this study effects of certain isolated fractions from root-bark of Berberis aristata on blood glucose levels were determined in normal and alloxan-diabetic rabbits. In normal rabbits, ethanolic fraction in 0.5, 1.0 and 1.5 g/kg produced significant decrease (P<0.05 or 0.001) at 8 and 12 hrs. Its acidified-basified fraction showed significant lowering of blood sugar at 2, 4, 8 and 12 hrs. The chloroform: methanol fraction also produced significant hypoglycaemic effect at these intervals. In alloxan-diabetic rabbits, ethanolic fraction in doses similar to normal animals produced significant decrease in blood glucose at 2, 4, 8 and 12 hrs. Also, acidified-basified fraction of the root-bark in 100 and 125mg/kg doses produced significant decrease in the levels at 2, 4 and 8 hrs. In these animals, its chloroform: methanol fraction (4 and 5mg/kg) produced significant effect at 8 and 12 hrs, while at the dose 6mg/kg body weight was found to be significant decrease blood glucose level at 2 and 4 hrs and highly significant decrease blood glucose level at 8 and 12 hrs interval. Gliclazide in 500mg/kg produced significant decrease blood glucose level at 2, 4, 8 and 12 hrs in normal rabbits only but not in alloxan-diabetics. Thus our data showed that the test fractions of B. aristata root-bark produce significant hypoglycaemia in both, normal and diabetic rabbits. These appear to be more potent hypoglycaemic than even gliclazide. In addition, it appears that active ingredients of this plant act by producing an organotropic effect on pancreatic β-cells, which results in increased release of insulin from the islets of Langerhans in the rabbits. These natural products also possess some insulin-like activity in alloxan-diabetic rabbits as alloxan has been reported to be a specific β-cytotoxic drug by complexing with the metal ions in the islets. However, further investigations are still needed to elucidate the mechanism of hypoglycaemic effect and to isolate the exact active principles of the B. aristata roots.