A simple wet chemical route has been used to synthesized the YMnO3, SrTiO3, and YMnO3/SrTiO3 composites. Their crystal structure, surface morphology, optical properties, electrochemical properties and photocatalytic activity were investigated by a series of characterization equipment. From these investigations, it was found that YMnO3 precursor introduced into SrTiO3 precursor solution improved the phase purity, optical properties, surface morphology and photocatalytic activity of SrTiO3 significantly. Nitrogen physisorption isotherms show that the obtained YMnO3, SrTiO3, and YMnO3/SrTiO3 composites possess high BET specific surface areas (100.21–158.97 m2 g−1) and mesoporous structure (pore size is about 20–25 nm). Photocatalytic experiment results suggest that the YMnO3/SrTiO3 composites exhibits high photocatalytic activities and robust stabilities toward to degradation of methyl red (MR) dye under visible light irradiation. In the p–n junction YMnO3/SrTiO3 composites, the excellent photocatalytic activity may be due to the surface defect promote charge carrier transfer.