Sixteen antioxidative compounds were purified and isolated from the aerial parts of Suaeda japonica by column chromatography using Amberlite XAD-2 and octadecylsilane columns and high-performance liquid chromatography. These compounds, esculin ( 1), citrusin D (2), scopolin (3), cichoriin (4), isorhamnetin 3-O-rutinoside-7-O-β-D-glucopyranoside (5), 3'-methoxytaxifolin 7-O-β-D-glucopyranoside (6), (+)-lyoniresinol 3a-O-β-D-glucopyranoside (7), (2R,3R,4S)-isolariciresinol 3a-O-β-D-glucopyranoside (8), N-cis-feruloyltyramine 4-O-β-D-glucopyranoside (9), N-cis-feruloylmethoxytyramine 4-O-β-D-glucopyranoside (10), trans-icariside H 1 (11), cis-icariside H 1 (12), N-transferuloyltyramine 4-O-β-D-glucopyranoside (13), rutin (14), kaempferol-3-O-rutinoside (15), and narcissin ( 16), were identified for the firtst time in S. japonica. The structures of these compounds were determined by mass spectrometry and nuclear magnetic resonance spectroscopic analyses. Among the compounds, 14 showed the highest 1,1-diphenyl-2-picrylhydrazyl free radical-scavenging activity and 8 exhibited the highest reactive oxygen species-scavenging activity in Huh7 cells.