In this paper, the inhibition of α-amylase and α-glucosidase by nine pentacyclic triterpenes was determined. For α-amylase inhibitory activity, the IC50 values of ursolic acid, corosolic acid, and oleanolic acid were 22.6±2.4μM, 31.2±3.4μM, and 94.1±6.7μM, respectively. For α-glucosidase inhibition, the IC50 values of ursolic acid, corosolic acid, betulinic acid, and oleanolic acid were 12.1±1.0μM, 17.2±0.9μM, 14.9±1.9μM, and 35.6±2.6μM, respectively. The combination of corosolic acid and oleanolic acid with acarbose showed synergistic inhibition against α-amylase. The combination of the tested triterpenes with acarbose mainly exhibited additive inhibition against α-glucosidase. Kinetic studies revealed that corosolic acid and oleanolic acid showed non-competitive inhibition and acarbose showed mixed-type inhibition against α-amylase. The results provide valuable implications for the triterpenes (ursolic acid, corosolic acid, and oleanolic acid) alone or in combination with acarbose as a therapeutic agent for the treatment of diabetes mellitus.