A polygalatenoside useful as an antidepressant agent having the formula is disclosed: wherein R, R' and R'' independently are H or R.sub.1, provided that R, R' and R'' are not all H, wherein R.sub.1 is wherein R.sub.2 is hydrogen, C1-C6 alkyl, C1-C6 alkoxy or halogen; or a pharmaceutically acceptable salt thereof. Preferably, R.sub.2 is H.