Multi-walled carbon nanotubes (MWNT) and TiO2 composite catalysts were prepared by a modified sol-gel method. The nanoscaled composite materials were extensively characterized by TG, N-2 adsorption-desorption isotherm, XRD, SEM, EDX, TEM and UV-vis spectra. The photocatalytic degradation of phenol was performed under visible light irradiation on these catalysts, An optimum of synergetic effect on photocatalytic activity was observed for a weight ratio MWNT/TiO2 equal to 20% with an increase in the first-order rate constant by a factor of 4.1. The synergetic effect, induced by a strong interphase interaction between MWNT and TiO2, was discussed in terms of different roles played by MWNT in the composite catalysts. (c) 2005 Elsevier B.V. All rights reserved.