A new megastigmane derivative, (6R,9S)-6′-(4′′-hydroxybenzoyl)-roseoside(1)and two known compounds, the biflavoneagathisflavone(2) and 4- hydroxybenzoic acid (3) were isolated and purified from leaves and stems of Ouratea polyantha Engl. Agathisflavone was isolated in a single high-speed counter-current chromatography run, while the megastigmane was purified in two steps, by using a combination of high-speed countercurrent chromatography and analytical column chromatography. All structures were elucidated on the basis of spectral evidence and comparison with literature data. Compound 1 was characterized by []D 20, UV-Vis, IR, MS, 1H NMR, 13C NMR, HMQC, HMBC, COSY and NOESY. Compounds 1 and 2 showed an inhibitory effect of 63.6 and 13.7% on the G-6-Pase intact microsomes, respectively.