The present invention aims to provide a pharmaceutical agent for the prophylaxis and/or treatment of Alzheimers disease, which has a novel action mechanism and shows less side effects. A polyphenol derivative having liposolubility enhanced by the introduction of at least one kind of a liposoluble group selected from the group consisting of a chain saturated hydrocarbon group, a chain unsaturated hydrocarbon group, a cyclic saturated hydrocarbon group, a cyclic unsaturated hydrocarbon group, an aromatic hydrocarbon group, a liposoluble vitamin residue and a sterol residue has an action to potentiate neprilysin activity, and is useful as a pharmaceutical agent for the prophylaxis and/or treatment of Alzheimers disease.
