The ethyl acetate (EtOAc) layer of Canavalia gladiata (sword bean) methanol extracts showed higher 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity than other layers. Four phenolic compounds were isolated from the EtOAc layer by silica gel column chromatography and prep-HPLC using a guided DPPH radical-scavenging assay. The isolated compounds were identified as methyl gallate (1), gallic acid (2), 1,6-di-O-galloyl β-D-glucopyranoside (3), and 1,4,6-tri-O-galloyl β-D-glucopyranoside (4) based on MS and NMR analyses. Among the four compounds, no. 4was isolated from this plant for the first time. Their DPPH radical-scavenging activities based on SC50 decreased in the following order: 4 (6.9 μM)>3 (8.3 μM)>2 (10.0 μM)>1 (10.3 μM).