One new megastigmane glycoside, ficalloside (1), and eleven known compounds, were isolated from methanol extract of Ficus callosa leaves by repeated column chromatography. Their structures were established on the basis of spectral and chemical evidence. The antioxidant activities of these compounds were measured using the oxygen radical absorbance capacity (ORAC) assay. Compound 8 exhibited potent antioxidant activity of 10.6 microM trolox equivalents at the concentration of 2 microM. At this concentration, compounds 4-7 and 9-12 showed significant antioxidant activity with ranging of 2.1-6.1 microM trolox equivalents.