The first phytochemical investigation of Polyalthia cinnamomea led to the isolation and identification of two new oxoprotoberberine alkaloids, (���)-(13aS)-polyalthiacinnamines A and B, together with eleven known compounds. The structures of the new compounds were elucidated by extensive spectroscopic methods. The absolute configuration of miliusacunine E and consanguine B was established by X-ray diffraction analysis using Cu K�� radiation and ECD spectra, whereas the absolute configurations of polyalthiacinnamines A and B were established by comparison of their ECD spectra and specific rotations with those of miliusacunine E and consanguine B. Compounds 1���4, 6, and 8 exhibited ��-glucosidase inhibitory activities (IC50 values ranging from 11.3 to 57.9 ��M) better than a positive control (acarbose, IC50 83.5 ��M). Compound 2 also exhibited NO production inhibitory activity with an IC50 value of 24.4 ��M (indomethacin, a positive control, IC50 = 32.2 ��M).