Titanium dioxide was modified with neodymium metal ion by a wet-chemical coprecipitation-peptization technique under low temperature to produce crystallized sol catalyst (Nd3+-TiO2). Crystal structure was characterized by X-ray diffraction measurement. Sol particle size was studied by means of particle size distribution measurement. Surface hydroxyl groups were determined using Fourier transform infrared spectroscopy. Photocatalytic reactivity of sol photocatalysts was investigated under ultraviolet and visible light irradiation. Photodegradation and photomineralization under ultraviolet and visible light excitation were studied in the TiO2 and Nd3+-TiO2 hydrosol reaction system. A photocurrent-time spectrum was also applied to characterize the electron-transferring efficiency in the process of self-sensitization and dye-sensitization photocatalysis reactions. As an application approach of sol catalyst, Nd3+-TiO2 sol was coated on a diffusing optical fibers bundle and the photocatalytic reaction was investigated in the immobilization fiber reactor. (c) 2005 Society of Chemical Industry.