The photocatalytic activity of TiO2 films preserved under different conditions was investigated in the gas-phase photocatalytic degradation of trichloroethylene (TCE), The photocatalytic activity of the TiO2 films was found to depend greatly on the preservation temperature and time. The TiO2 films washed with water and then preserved at room temperature exhibited low photocatalytic activity compared with those that were unwashed. When the preservation time of the TiO2 films was long, their photocatalytic activity decreased, irrespective of the preservation conditions. The catalyst that is deactivated due to the long preservation time can be regenerated by UV preillumination.