Truffle-shaped Cu nanoparticles (NPs) were synthesized by photoreduction of copper acetate solution in the presence of TiO2. X-ray diffraction measurement revealed that the obtained NPs were composed of pure Cu without oxides, which was notable because the photoirradiation was performed under atmospheric conditions, where the Cu NPs are easily oxidized. The Cu NPs were dispersed stably without protectants because the TiO2 NPs adsorbed on the Cu NPs were dispersed, probably due to their electric repulsion.