Five distinct organic compounds with protected and unprotected phenolic hydroxyl groups were screened for their a-glucosidase inhibitory potential. Of these compounds, 2,4,6-trihydroxybenzaldehyde (THB) showed the strongest noncompetitive a-glucosidase inhibition (IC50 = 4.60 lM) and the most powerful antioxidant activity (DPPH assay) (IC50 = 71.4 lM) in vitro. In in vivo studies, THB significantly reduced blood glucose levels in normal and diabetic rats after glucose load compared to maltose load.