In this paper, Mn-Fe bimetallic nanoparticles were synthesized by simultaneous reduction of a salt mixture of KMnO4 and FeCl3 with glucose as a reducing agent. Degradation of methyl orange in aqueous solution, using hydrogen peroxide as an oxidizing agent, was used to evaluate the catalytic activity of the material. The material was characterized using scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. The results showed that cubic manganese oxide nanoparticles were formed at the molar ratio of KMnO4/C6H12O6·H2O = 5/5 and the hydrothermal temperature of 120-220°C, while the oval-shaped structure was formed at the molar ratio of KMnO4/C6H12O6·H2O = 5/40 and the hydrothermal temperature of 220 °C. The cubic Mn-Fe bimetallic nanoparticle was still formed at the molar ratio of Mn/Fe/C6H12O6 = 5/2/5 and the hydrothermal temperature of 120°C, and the methyl orange decomposition efficiency was found to be the highest value of 57% on this catalyst sample.