Highly aligned WO3 nanotrees are grown on metal tungsten by a simple hydrothermal reaction. Pd nanoparticles are selectively deposited on the WO3 nanotrees by a photocatalytic reduction reaction. Photocatalytic oxidation activity depends strongly on the position of the deposited Pd nanoparticles, and the WO3 nanotrees with Pd nanoparticles deposited at the bottom position exhibited efficient super-hydrophilicity.