The incidence of diabetes mellitus increases globally at an alarming rate with its consequent complications, despite the existing pharmacotherapy. There is current interest in the search for novel antidiabetic agents from medicinal plants. Combretum dolichopetalum is used in folkloric medicine for the management of diabetes. The root has been investigated for this activity but the leaf has not been studied. This study is therefore aimed at investigating the antidiabetic activity of the leaf. The hypoglycemic activity was studied in normoglycemic rats by administering the methanol extract (CME) orally to the rats at 100, 200 and 400 mg/kg. The fasting blood glucose (FBG) was monitored for 9 h. The CME was also administered (p.o.) daily to alloxan induced diabetic rats at the three dose levels for 14 days. The FBG was monitored for 9 h in day 1 and also at days 7 and 14. Glibenclamide was used as a reference drug. Phytochemical analysis was done by the standard procedures. Results show that the CME did not produce any significant (p < 0.05) reduction in the FBG of the normoglycemic and the diabetic rats in 9 h. The CME, however, produced a dose-dependent significant (p < 0.001) lowering of the FBG of the diabetic rats in 7 and 14 days, normalizing the FBG within the periods. The effect of the extract, especially at 400 mg/kg, was comparable to glibenclamide. Presence of alkaloids, flavonoids, tannins, glycosides, steroids and terpenoids was observed. The study has shown that the leaf of C. dolichopetalum possesses antidiabetic activity.