To study the chemical constituents of Alchornea trewioides, silica gel column chromatography, Sephadex LH-20, reverse phase ODS column chromatography, MCI and semi-preparative HPLC were used to separate the 95% EtOH extract of the root of Alchornea trewioides. The structures were elucidated on the basis of spectroscopic studies including ESI-TOF-MS, 1H NMR, 13C NMR, HSQC and HMBC. Eight phenolic acids were obtained and identified as 1-O-galloyl-6-O-vanilloyl-beta-glucose (1), gallic acid (2), ethyl gallate (3), syringic acid (4), glucosyringic acid (5), erigeside C (6), 3, 4-dimethoxyphenyl-(6'-O-alpha-L-rhamnosyl)-beta-D-glucopyranoside (7) and 3, 4, 5-trimethoxyphenyl-(6'-O-galloyl)-O-beta-D-glucopyranoside (8). Among them, compound 1 is a new compound, compounds 4-8 are isolated from the genus Alchornea for the first time, and the others are isolated from the plant for the first time.