In the present work, the TiO 2 films doped with 0–0.602at.% Gd were deposited by DC reactive magnetron sputtering and annealed in ambient air at 127302K. The effects of Gd concentration on crystal phase formation and subsequent changes in optical and photocatalytic properties were determined. Photoluminescence (PL) spectra and their correlation with electronic structure were described. Structural studies revealed that Gd doping in the TiO 2 lattice led to a low anatase thermal stability relative to pure TiO 2 . A study based on a joint use of PL and XPS analyses showed the enhancement of oxygen vacancy concentration in the Gd-doped TiO 2 films. Photocatalytic activity was dependent on Gd doping and phase structure. A suitable amount of Gd doping (0.3–0.402at.%) was favorable to the creation of abundant oxygen vacancies, so that the films could show an improvement in photocatalytic activity. After annealing, the photocatalytic activity of the films decreased with the increase of Gd content, due to the occurrence of the rutile phase.