The nanoparticles of Yb3+-doped (0.125 wt.%) and pure TiO2 were prepared by an acid-catalyzed sol-gel method and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance spectroscopy, and surface photovoltage spectroscopy; the specific surface of the samples was measured using the Brunauer-Emmett-Teller (BET) method. The photocatalytic degradation of methylene blue in aqueous solution was used as a probe reaction to estimate the photocatalytic activity of the prepared nanoparticles. The photocatalytic activity of Yb3+/TiO2 composite nanoparticles is much higher than that of pure TiO2. A low amount of Yb3+ in TiO2 can inhibit the anatase-rutile phase transformation of TiO2, prevent grain growth increasing the specific surface area, and favor the high-temperature stabilization of the pores. According to the surface voltage spectroscopy data, Tb3+-doping prevents recombination of photoinduced electrons and holes and improves the light absorption capacity of the particle surface.