Antioxidant activity of hydroxylated fullerenes, so-called fullerenols, against lipid peroxyl radical was evaluated by β-carotene bleaching assay. All samples showedmoderate to high antioxidant activity (%AOA), especially for C60(OH)12 (70.1) and C60(OH)44 (66.0) as compared with 8, 24, 26, and 36 hydroxylated ones (31.7-62.8).The detection of the possible products was conducted in the model reaction of both fullerenols and C60 with methyl linoleate by MALDI-TOF-MS. These results suggested that the two possible mechanisms, such as C-addition to double bonds and H-abstraction from-OH groups, are involved in the present radical scavenging reaction. [ABSTRACT FROM AUTHOR]