La-doped TiO_2 thin films on titanium substrates were prepared by the sol–gel method with titanium tetrachloride as a precursor and La_2O_3 as a source of lanthanum. The heat-treatment temperature dependence of the photoelectrochemical performance of the La-doped TiO_2 film in 0.2 mol/L Na_2SO_4 was investigated by the MottSchottky equation, electrochemical impedance spectroscopy, and the open-circuit potential test. The results from the Mott-Schottky curves show that the obtained films all were n-type semiconductors, and the film at 300 °C had the highest conduction band position and the widest space charge layer. The electrochemical impendence spectroscopy(EIS) tests of the 300 °C film decreased most during the change from illuminated to dark. The potential of the La–TiO_2 thin film electrode was the lowest after the 300 °C heat treatment. The open-circuit potential indicated that the photoelectrical performance of the La-TiO_2 films was enhanced with the addition of the La element and the largest decline(837.8 mV) in the electrode potential was achieved with the 300 °C heat treatment. La-doped TiO thin films on titanium substrates were prepared by the sol-gel method with titanium tetrachloride as a precursor and La 2 O 3 as a source of lanthanum. The heat-treatment temperature dependence of the photoelectrochemical performance of the La-doped TiO 2 film in 0.2 mol / L Na 2 SO 4 was investigated by the Mott Schottky equation, electrochemical impedance spectroscopy, and the open-circuit potential test. The results from the Mott-Schottky curves show that the obtained films all were n-type semiconductors, and the film at 300 ° C had the highest conduction band position and the widest space charge layer. The electrochemical of the TiO 2 thin film electrode was the bottom of the 300 ° C film decreased from illuminated to dark. after the 300 ° C heat treatment. The open-circuit potential indicated that the photoelectrical performance of the La-TiO 2 films was enhanced with the addition of La el ement and the largest decline (837.8 mV) in the electrode potential was achieved with the 300 ° C heat treatment.