To efficiently separate polyphenols from an extracted liquid of a plant using an adsorbent capable of selectively adsorbing polyphenols.

A plant extract liquid such as extracted tea obtained by decocting tea leaves is brought into contact with a weakly basic anion exchange resin to selectively adsorb the polyphenols such as tea catechin to the weakly basic anion exchange resin. The polyphenols adsorbed to the anion exchange resin are desorbed by using a sodium hydroxide solution, etc., as a desorbing liquid to obtain the liquid containing desorbed tea catechin. The weakly basic anion exchange resin is preferably an HCO3--type resin prepared e.g. by blowing carbon dioxide gas. The desorbed liquid is preferably neutralized to pH 2-6 or thereabout by the addition of an acid.