In this study, methanol leaf extract of Pterocarpus osun and its fractions were assessed for anti-diabetic ability using in vitro α-amylase inhibitory potential and antioxidant activities determined by DPPH radical scavenging effect, reducing power and total phenolic content. Our results showed that the extract had a dose dependent prevention of digestion of carbohydrates by inhibiting α-amylase. The maximum effect was observed at 2.0mg/ml was (74.98±4.35%, P<0.05). At 0.2mg/ml, the aqueous

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... tion demonstrated 71.87±3.41% inhibition which is comparable to 88.10±4.59% of acarbose used as reference drug. The hexane and chloroform fractions demonstrated lower (P<0.05) inhibitory activity; 16.16 and 14.34% respectively. The total phenolic content of the P. osun extract measured using Folin Ciocalteu reagent in terms of gallic acid equivalent (GAE) was found to be 97.01±0.02mg/g. The DPPH radical scavenging activity of the extract increased with concentration but was significantly less than (P<0.05) ascorbic acid used as positive control. The radical scavenging activity of the aqueous fraction (94.60±3.45%) at 0.2mg/ml was however higher than that of reference drug. The hexane and chloroform fractions however showed lower radical scavenging activity; 12.35±0.07 and 46.20±1.23% respectively. The extract showed dose-dependent increase in reducing power. The aqueous fraction however showed highest reducing ability while the n-hexane fraction had lowest. This study indicates that α-amylase inhibitory and antioxidant activities of the methanol extract of P. osun resides in the aqueous fraction.