Novel antimicrobial substance was isolated from seed coat of Canavalia gladiata by extraction with 75% methanol. Isolation and purification were conducted with solvent fractionation and chromatography on silica gel and sephadex LH-20 columns. Each fraction of antimicrobial activity was tested by paper disc method. Single compound was obtained from the 4th fraction of sephadex LH-20 column chromatography using chloroform/methanol (1:4, v/v), and identified as 3,4,5-trihydroxybenzoic acid methyl ester (methyl gallate) based on HPLC, GC/MS, FT-IR, $^1H$ NMR, and $^{13}C$ NMR analyses. This is the first report describing the presence of methyl gallate in C. gladiata.