A simple method for preparing nanocrystalline C-N-codoped TiO2 photocatalyst was developed by annealing titanium carbonitride. The prepared C-N-codoped TiO2 powders were characterized by TGA, XRD, XPS, UV-Vis, PL, SEM, and BET surface areas. The photocatalytic activity was evaluated by the photocatalytic degradation of methylene blue in an aqueous solution under visible-light radiation. Results showed that the annealing temperatures and time affected the crystal composition and structure and activity of the catalyst. The most promoting effect of C-N-codoping in activity was obtained over C-N-codoped TiO2 prepared by annealing titanium carbonitride at 400 A degrees C for 8 h. The high photocatalytic activity could be attributed to the synergetic effects in light absorption and the suppression of recombination of electrons/holes pairs.