The metallic Cu nanoparticles have been successfully deposited on the heterogeneous TiO2 surface by the borohydride reduction of copper nitrate in water/CH3CN mixture under Ar atmosphere. The catalytic activity of the Cu-TiO2 nanocomposite was evaluated by the application to a photocatalytic cancer cell-killing under UV-visible light irradiation. Based on the obtained results, a plausible mechanism was proposed.