Placolobium vietnamense N. D. Khoi & Yakovlev, known as ‘Rang rang Viet’ in Vietnam, is an indigenous perennial plant distributed in Dak Nong and Kontum provinces, belonging to four species of the genus Placolobium (Fabaceae) found in Vietnam. Although the plant has been used as folk remedies for snakebites, debility, to increase strength after childbirth or to treat a number of other diseases, however, there still have been few studies on its chemical constituents. This paper presented the investigation on the chemical composition of the fraction 6 of the n-hexane of the stems of Rang rang Viet, collected at Dak Nong provinceresulted in the isolation of six compounds being determined as mackaiin (1), medicarpin (2), 3,9-dimethoxy-6a-hydroxypterocarpan (3), caviunin (4), daidzein (5) and aloe-emodin (6). Their chemical structures were elucidated by MS, 1D, and 2D–NMR as well as compared with data in the literatures. The isolated compounds were also investigated for their α-glucosidase inhibitory activity. The results showed that six compounds were more active than acarbose, with IC50 values of 11.0 – 32.8 μg/mL. All isolated compounds were reported for the first time in the genus Placolobium.