4-Methyl-8-hydroxylpsoralen (MXan) and 4,9-dimethyl-8-hydroxylpsoralen (DMXan) were synthesized in order to clarify the effect of methyl on the antioxidant effectiveness of xanthotoxol (8-hydroxylpsoralen, Xan), which were assessed by bleaching β-carotene in linoleic acid–Triton emulsion, by interacting with 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) cationic radical (ABTS + ), 2,2′-diphenyl-1-picrylhydrazyl radical (DPPH), and galvinoxyl radical, and by protecting DNA against the oxidation induced by Cu 2+ /glutathione (GSH) and 2,2′-azobis(2-amidinopropane hydrochloride) (AAPH). Methyl attaching to xanthotoxol did not affect its ability to protect linoleic acid against autoxidation and to inhibit Cu 2+ /GSH-induced oxidation DNA, but decreased its ability to scavenge ABTS + and DPPH, and to protect DNA against AAPH-induced oxidation. Therefore, methyl attenuated the antioxidant effectiveness of xanthotoxol in radical-induced oxidation of DNA.