The study was performed to compare the blood glucose lowering effect of Swietenia mahagoni seeds with an oral antidiabetic drug, rosiglitazone in experimentally induced diabetic rats. Twentyfour healthy Long Evans Norwegian strain of rats were included in the study and divided into four groups (A, B, C and D) comprising 6 rats each. Group A (control group) received standard rat food for 14 days. Diabetes was induced by a single intraperitoneal administration of alloxan 120 mg/kg body weight in Group B, C and D. Group B was given standard food for 10 days and considered as diabetic control. Group C and D were treated with ethanolic extract of Swietenia mahagoni seeds 1000 mg/kg and rosiglitazone 10 mg/kg orally respectively. Administration of ethanolic extract of Swietenia mahagoni seeds in group C and rosiglitazone in group D produced a significant reduction in blood glucose level as compared to diabetic control (group B). Histological examination of pancreas showed destruction of beta cells in Islets of pancreas in group B whereas retaining of islets and few degranulations of beta cells of pancreas found in group C and group D. The observations and results of the present study provide information that ethanolic extract of Swietenia mahagoni seeds has hypoglycaemic effect in experimentally induced diabetic rats which requires further investigation.