A new octadecatrienoic acid and a new benzyl glycoside, along with a known compound, were isolated from the leaves of Smallanthus sonchifolius. The structures of the two new compounds were elucidated as 13(R)-hydroxy-octadeca-(9E,11E,15Z)-trienoic acid (1) and benzyl alcohol 7-O-alpha-L-arabinopyranosyl(1" --> 2')-beta-D-glucopyranoside (2) on the basis of spectroscopic analysis and chemical evidence. The known compound was identified as 13(R)-hydroxy-octadeca-(9Z,11E,15Z)-trienoic acid (3) by comparison of its spectral data with that reported. Compound 3 was isolated for the first time from the title plant.