Time-resolved EPR spectra were observed by means of the transient EPR technique for two kinds of fullerene dimers C-120 and C120O in the lowest excited triplet (T-1) states and compared with those of mono-adducts of fullerene (C-60). It was found that zero-field splitting (zfs) parameters of both dimers are nearly the same as those of the monomers, indicating that the excitation is almost completely localized at one of the two fullerene units in the T-1 state. (C) 2002 Elsevier Science B.V. All rights reserved.