To provide a polyphenol-content-increasing agentwhich increases the content of polyphenol in a plant.polyphenol-content-increasing agent for plant,containing, as the active ingredient, a 5-aminolevulinicacid or a derivative thereof represented by the followingformula (1):(Chem 1)R2R1NCH2COCH2CH2COR3 (1)wherein R1 and R2 each independently represents a hydrogenatom, an alkyl group, an acyl group, an alkoxycarbonylgroup, an aryl group, or an aralkyl group； R3 represents ahydroxyl group, an alkoxy group which may have asubstituent, an acyloxy group, an alkoxycarbonyloxy group,an aryloxy group, an aralkyloxy group, or an amino group,or a salt thereof.
