The antioxidant activity and the variations of components in methanolic extracts of peanut hulls (MEPH) after UV irradiation were investigated. MEPH of varied periods of irradiation (0, 3 and 6 days), exhibited 96.0% inhibition of peroxidation of linoleic acid. The relative remaining ratios of luteolin in MEPH after irradiation for 3 and 6 days were 87.9% and 69.5%, respectively, and those of total phenolic compounds were 96.5% and 90.4%, respectively. MEPH irradiated for 0, 3 and 6 days exhibited a similarly marked antioxidant activity as a result of a large content of total phenolic compounds. MEPH of varied periods of irradiation always showed the same UV-vis spectra and Rf values on a TLC plate. Thus the antioxidant activity of MEPH was unaffected by UV irradiation.