Among 38 Vietnamese medicinal plant extracts investigated for their ${alpha}$-glucosidase inhibitory activity, 35 extracts showed $IC_{50}$ values below $250{mu}g/mL$. The MeOH extracts of the heartwood of Oroxylum indicum, the seeds of Caesalpinia sappan, and the fruits of Xanthium strumarium exhibited strong ${alpha}$-glucosidase inhibitory activity with $IC_{50}$ values less than $50{mu}g/mL$. Fractionation of the MeOH extract of the heartwood of O. indicum led to the isolation of oroxylin A (1), oroxyloside (2), hispidulin (3), apigenin (4), ficusal (5), balanophonin (6), 2- (1-hydroxymethylethyl)-4H,9H-naphtho[2,3-b]furan-4,9-dione (7), salicylic acid (8), p-hydroxybenzoic acid (9), protocatechuic acid (10), isovanillin (11), and ${eta}$-hydroxypropiovanillon (12). Compounds 1 - 3, 5, 6, 8, 10, and 12 showed more potent activities, with $IC_{50}$ values ranging from 2.13 to $133.51{mu}M$, than a positive control acabose ($IC_{50}$, $241.85{mu}M$). The kinetic study indicated that oroxyloside (2) displayed mixed-type inhibition with inhibition constant (Ki) was $3.56{mu}M$.