The structure of isomartynoside, a new phenylpropanoid glycoside, isolated along with the known martynoside from Galeopsis pubescens, has been elucidated on the basis of chemical and spectral data as 3-hydroxy-4-methoxy-β-phenylethoxy-O-α-L-rhamnopyranosyl-(1 → 3)-6-O-feruloyl-β-D-glucopyranoside.