A new octanordammarane triterpene, 3β,15α-dihydroxymansumbinol (1) and a novel A-ring contracted oleanane triterpenoid, 2-formyl-(A)1-19α-hydroxy-1-norolean-2,12-dien-28-oic acid (2) were isolated from the roots extract of Rosa rugosa along with fifteen known compounds (3-17). Their structures were elucidated by extensive spectroscopic analysis, including 1D and 2D NMR, and FTICRMS. The MeOH extract, as well as CH2Cl2 and EtOAc fractions at a concentration of 0.5mg/mL showed potent sucrase inhibitory activity, with inhibition percentage values of 84.67±5.37%, 87.50±2.78%, and 81.91±2.90%, respectively. In addition, compounds 7-13 (1.0 mM) showed potent sucrase inhibitory activity (61.88±3.19% to 84.70±3.07% inhibition), which was comparable to that of the positive control, acarbose, with an inhibition percentage value of 50.96±2.97%. Compounds 1, 2, 4, and 14-17 showed moderate and/or weak inhibitory activities at the same concentration. The α-glucosidase inhibitory activities of the extracts and purified compounds may provide a novel opportunity to develop a new class of antidiabetic agents.