To modify the surface of vapor grown carbon fiber (VGCF), poly(ethylene-block-ethylene oxide) (PE-b-PEO, M-n = 1400, PEO content = 50 wt%) was successfully grafted onto the surface by using gamma-ray irradiation of the PE-b-PEO-adsorbed VGCF in solvent-free system. It is found that the percentage of polymer grafting reached 15.0% when the PE-b-PEO-adsorbed VGCF was irradiated by gamma-ray over 40 kGy dose at 110 degreesC, but at the lower irradiation temperature of 75 degreesC, the grafting reaction scarcely proceeded. This indicates that polymer radicals formed by gamma-ray irradiation were successfully trapped by VGCF surface above melting point of PE-b-PEO. On the other hand, when the dispersion of VGCF in THF solution of PE-b-PEO was irradiated, the percentage of PE-b-PEO grafting was less than 4.0%. It was confirmed by a field-emission scanning electron microscope (FE-SEM) that the surface of the VGCF was uniformly covered by grafted PE-b-PEO. In addition, the surface free energy of ungrafted and PE-b-PEO-grafted VGCF was determined. (C) 2003 Elsevier Science Ltd. All rights reserved.