By various chromatographic methods, one new phenylpropanoid glycoside, heterosmilaside (1), two known phenylpropanoid glycosides, helonioside B (2), and 2',6'-diacetyl-3,6-diferuloyl sucrose (3), and three known flavonoids, isoquercetin (4), quercetin-3-O-beta-D-glucuronopyranoside (5), and quercetin-3-O-(2''-alpha-L-rhamnopyranosyl)-beta-D-glucuronopyranoside (6) were isolated from the methanolic extract of the aerial part of Heterosmilax erythrantha Baill. Their structures were elucidated on the basis of spectroscopic analyses. All the isolated compounds were tested for antioxidant activity in the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay. Among them, compounds 5 and 6 showed significant antioxidant activity with SC(50) values of 3.7 and 6.5 microg/mL, respectively.