The applicability of LaMnO3 perovskite as nanocatalyst was investigated for removing of methylene blue as a model compound of organic pollutant under visible light and ultrasonic irradiation simultaneously. The LaMnO3 perovskite was synthesized by co-precipitation method and it was characterized in terms of morphological, structural, compositional, optical and magnetic properties. The detailed characterization confirmed that LaMnO3 perovskite had a single-phase orthorhombic structure with estimated crystallite size of 44 nm. UV-vis diffuse reflectance spectra showed a weak reflection with small band gap energy. The weak ferromagnetic behavior with a saturation magnetization of 3 emu/g was obtained at 1 Tesla. The photosonocatalytic showed significantly higher catalytic activity in decomposing methylene blue compared to that of sonocatalytic or photocatalytic alone. Radical scavenger experiments revealed that holes were the predominant oxidative species involved in the process.