An object of the present invention is to provide a method that can effectively/efficiently increase the amount of a phenolic compound such as a polyphenol. The invention provides a method for increasing an amount of a phenolic compound in a plant, or a method for producing a plant containing an increased amount of a phenolic compound, the method comprising irradiating the/a plant with ultraviolet light, wherein a fluence at wavelengths of 270 to 290 nm is 1500 to 50000 μmol/m2 and a fluence at wavelengths of 310 to 400 nm is less than 50% of that at wavelengths of 270 to 290 nm.