In this paper, p-type CuInS2 quantum dots are synthesized by a solvothermal route and incorporated with n-type TiO2 nanoparticles by a thermal treatment process. Transmission electron microscopy (TEM) results indicate that the CuInS2 quantum dots distribute uniformly and the size is similar to 3.4 nm. Photocatalytic activities of the TiO2 nanoparticles sensitized with the CuInS2 quantum dots are evaluated by the degradation of the methyl orange aqueous solution under ultraviolet (UV) and visible (vis) light irradiation and show an enhanced performance, compared with the pure TiO2 nanoparticles and the pure CuInS2 quantum dots. Microstructural, morphological, and optical properties of the TiO2 nanoparticles sensitized with the CuInS2 quantum dots are characterized by X-ray diffraction (XRD) analysis, TEM, and UV-vis absorption spectroscopy. Results indicate that the CuInS2 quantum dots greatly enhance the absorption of UV and visible light due to the p-n heterojunction being constructed between p-type CuInS2 quantum dots, and n-type TiO2 nanoparticles. Effects of the mass ratio of the TiO2 and CuInS2 and the thermal treatment temperature on the photocatalytic activities of the TiO2 nanoparticles sensitized with the CuInS2 quantum dots are also investigated.