A key strategy to mitigate postprandial hyperglycemia involves inhibiting α-amylases, which commence the starch digestion process in the gut. This study examined the inhibitory effects of resveratrol and stilbenoid tetramers, vaticanol B, (-)-hopeaphenol, and vatalbinoside A on human salivary and pancreatic α-amylases experimentally and through molecular docking studies. Vaticanol B demonstrated the most potent inhibition with IC50 values of 5.3 ± 0.3 μM for salivary and 6.1 ± 0.5 μM for pancreatic α-amylase (compared to acarbose with IC50 values of 1.2 ± 0.1 μM and 0.5 ± 0.0 μM, respectively). Kinetic analysis suggested a competitive inhibition mode for vaticanol B. Resveratrol and vatalbinoside A were poor inhibitors of human α-amylases, while (-)-hopeaphenol exhibited moderate inhibition. Molecular docking supported the inhibition data, and several aspects of the structural configurations explained the stronger inhibition exerted by vaticanol B. Overall, vaticanol B shows promise as a natural alternative to acarbose for inhibiting α-amylase.