The 50% aqueous methanolic extract from the bark of Betula platyphylla SUKATCHEV var. japonica (MIQ). HARA was found to show potent inhibitory activity on the liver-injury induced by CCl4 or D-galactosamine (D-GalN)/lipopolysaccharide as well as O2- scavenging and antioxidative activities. From the 50% aqueous methanolic extract, two new diarylheptanoids named betulaplatosides Ia (1) and Ib (2) and a new arylbutanoid named betulaplatoside II (3) were isolated together with seventeen known aromatic constituents. 1, 2, and two known diarylheptanoids [(5S)-5-hydroxy-1,7-bis-(4-hydroxyphenyl)-3-heptanone 5-O-beta-D-apiofurano-syl-(1-->6)-beta-D-glucopyranoside (6) and aceroside VIII (7)] showed protective activity against D-GalN-induced cytotoxicity in primary cultured rat hepatocytes. Furthermore, several aromatic constituents exhibited potent O2- scavenging and antioxidative activities.