TiO2/CNTs nanocomposites with different Ti/C molar ratios were prepared by a sol-hydrolysis method at 368 K, using titanium tetrachloride as a precursor and nitrified carbon nanotubes as a support. The crystal phase, morphology and microstructure of the sample were characterized by X-ray Diffraction (XRD) and High-Resolution Transmission Electron Microscope (HRTEM). The photocatalytic activity of the samples was performed by methyl orange in aqueous solutions under UV light.The supernatant liquid of methyl orange during degradation was determined by using an UV-vis spectrophotometer (UV-vis). XRD results show that the crystal phases of the sample are composed of carbon nanotubes, anatase and rutile. HRTEM results show that the average diameter of oval titania is about 4.2 nm, and it decorates on the surface of carbon nanotubes uniformly. UV-vis results show that the photocatalytic activity of the TiO2/CNTs nanocomposite with the optimum Ti/C molar ratio is much higher than that of P25. These results indicate that a synergistic effect exists between titania and carbon nanotubes in the nanocomposite.