A chemical examination of the phenolic compounds in the leaves of Sapium japonicum(Euphorbiacesae) has led to the isolation of eleven phenolic compounds, containing five hydrolysable tannins and six flavonoids. On the basis of chemical and spectroscopic evidences, the structures of these compounds were confirmed to be gallic acid(1), 5-O-caffeoyl quinic acid(2), 1-O-galloyl-3,6-(R)-HHDP-${\beta}-_D$-glucose(corilagin)(3), 1-O-galloyl-2,4(R)-DHHDP-${\beta}-_D$-glucose(furosin)(4), 1-O-galloyl-2,4-(R)-DHHDP-3,6-(R)-HHDP-${\beta}-_D$-glucose(geraniin )(5), astragalin(6), trifolin(7), afzelin(8), quercetin(9), isoquercitrin(10) and rutin(11). Among them geraniin was the main component.