Four new compounds, (+)-(2S)-desmosdumosone (1), (+)-(2R)-7,8-dimethoxy-5-hydroxyflavanone (7), (+)-(2R)-7-methoxychamanetin (9), and (+)-(1ˊR,2ˊR)-phebalosin (18), and 25 known compounds were isolated from the twig and leaf extracts of Desmos dumosus. Compounds (±)-7 and (±)-9 were isolated as racemates and their enantiomers were separated by chiral HPLC. Their structures were elucidated by spectroscopic methods as well as comparisons made from the literature. The absolute configuration of (+)-(1ʹR,2ʹR)-18 was established by X-ray diffraction analysis using Cu Kα radiation and electronic circular dichroism (ECD) spectoscopy. In contrast, the absolute configuration of compounds (+)-(2S)-1, (+)-(2R)-7, and (+)-(2R)-9 were identified by comparing their ECD spectra and specific rotations with those of reported known compounds. Compounds 9, 11, 13, 14, 22, 25, and 28 showed α-glucosidase inhibitory activities with IC50 values ranging from 5.3-52.7 μM, much better than that of standard control (acarbose, IC50 value 83.5 μM). Compound 13 was the most active with an IC50 value of 5.3 μM.