1-Naphthol has been used as an in situ fluorescent probe to characterize the surface physicochemical properties of carbon nanofibers (CNFs). The fluorescence of I-naphthol adsorbed on untreated CNFs originates from the L-1(b) state and its peaks are shifted by the polarity of the surrounding media, indicating that there is a relatively non-polar area on the CNF surface. 1-Naphthol interacting with oxidized sites on the surface of nitric acid-treated CNFs exhibited an ion-pair fluorescence. This shows that there are some functional groups, interacting with I-naphthol, on the treated CNF surface. The surface physicochemical properties of the CNFs can be characterized by this fluorescent probe. (C) 2004 Elsevier B.V. All rights reserved.