In present study hypoglycaemic effects of the crude powdered C. decussata and its methanolic extract (ME) in alloxan diabetic rabbits were evaluated. The hypoglycaemic effect was measured by blood glucose, insulin level, HbA1c and his to pathology of pancreas. Glucose lowering effect of the ME was studied in diabetic rabbits. The effects of extract on blood glucose, body weight, food in take, fluid intake, OGTT were also evaluated. The results showed that 0.5,1 and 2g/kg of the powder significantly decreased blood glucose levels in normal rabbits and diabetic rabbits at the intervals checked. Oral intake of pioglitazone also reduced the levels in these rabbits. Synergistic hypoglycaemic effect of 600mg/kg of ME with different doses of insulin (2 & 3unit/kg, s/c) further reduced blood glucose levels of treated alloxan-diabetic rabbits. The oral glucose tolerance test revealed lowered area under curve values in ME treated rabbits. Treatment with ME (400 and 600 mg/kg) for 30 days showed highly significant decrease in blood glucose level by augmenting insulin secretion, HbA1cand significant increase in body weight, serum insulin levels in treated diabetic rabbits. Histopathology study showed regeneration of β-cells. These studies have, therefore, supported the traditional use of this herb in diabetic patients.