Fullerenes C 60 and C 70 are shown to react with Hg(CF 3 COO) 2 in the ionization chamber of the electron impact source of a mass spectrometer at 300 and 310uC, yielding trifluoromethylated derivatives of the fullerenes with up to six and two CF 3 addends, respectively. For some of the products the reactions are accompanied by hydrogen addition. Based on previous mechanistic studies of the analogous reactions of C 60 with the Scherer radical (C 9 F 19 N), a mixture of perfluoronones (C 9 F 18 ), and acetone, a plausible scheme is proposed for the processes. It involves formation of the intermediate CF 3 radicals owing to electron impact or thermally initiated homolytic dissociation of the mercury(II) salt, and their further reaction with the fullerenes at the surface of the ionization chamber. Heating mixtures of the reagents under argon at 300-310uC also yields trifluoromethylated fullerenes, in agreement with the results obtained with the ionization chamber.