Magnetic mesoporous Mn-Fe oxide catalyst with high surface area was prepared by calcining the corresponding oxalate precursor. The calcined sample was characterized by XRD, FTIR, N2 adsorption, TEM, and SEM. The catalytic property of the porous Mn-Fe oxide catalyst was evaluated by catalytic decolorization of methyl orange (MO). XRD, SEM, and TEM analysis and N2 adsorption–desorption isotherm revealed mesoporous Mn-Fe oxide strucutre with high-surface area and uniform pore-size distribution. The results of catalytic performance measurements showed that the Mn-Fe binary oxide was an effective catalyst. The as-prepared catalyst could be recycled as a magnetically separatable catalyst to treat dye-containing wastewater.