The inhibitory activity of several crude drugs on $alpha$-glucosidases, which are the key enzymes for carbohydrate digestion and the prevention of diabetic complications, was investigated. Several crude drugs including Terminaliae Fructus, Mori Cortex Radicis, Caesalpiniae Lignum and Cyrophora esculenta potently inhibited maltase and sucrase isolated from rat intestine, while Arecae Semen and Corni Fructus remarkably inhibited $alpha$-amylase. Caesalpiniae Lignum and Gyrophora esculenta exhibited significant reductions of blood glucose elevation in mice loaded with maltose and sucrose.