•Sr doped LaMnO3 nanoparticles were prepared by microwave combustion method.•La0.6Sr0.4MnO3 nanopowder has small bandgap with excellent phototacalytic property.•The nanoproducts show super-paramagnetic with high magnetization of 57 emu/g.•Sr doped LaMnO3 nanoproduct is a potential recyclable photocatalyst of high efficient. Lanthanium manganite (LaMnO3) is an interesting perovskite material with many practical applications in various fields. In the present work, LaxSr1-xMnO3 (x = 0.2–0.4) nanopowder was prepared by a single step microwave combustion process without any post annealing requirements. The as-prepared nanoproducts were characterized with different measurements such as X-ray diffraction, scanning electron microscopy, diffuse reflectance, Raman scattering and magneto vibrating sample. The nanoproducts of high crystal quality showed small bandgap of about 2.2 eV, which is very useful for visible photocatalytic activity. The obtained nanoparticles also possess excellent photocatalyst activity in visible light, which is demonstrated by ability to degrade up to 96% of methylene blue 10 ppm after 120 min of irradiation with visible light. Sr doped LaMnO3 nanoparticles also exhibit superparamagnetic property with high magnetization of 57 emu/g, which opens recyclable ability in water treatment application of the synthesized nanopowder.