The possibility of an organometal halide perovskite, CH3NH3PbBr3, was investigated as a cosensitizer to a Ru-complex dye and an alkoxysilylcoumarin dye in dye-sensitized solar cells. The perovskite was found to work as the cosensitizer effectively, and the light-to-electric energy conversion efficiencies of the cells were improved more than 10% by the cosensitization under the present test conditions.