Abstract A highly efficient method has been reported to fabricate the reduced graphene oxide/MnO2 (RGO/MnO2) hybrid materials, a kind of catalysts for oxidative decomposition of methylene blue (MB). The pristine suspension of graphene oxide/manganese sulfate (GO/MnSO4) produced by the modified Hummers method is in situ transformed into GO/MnO2 composites in combination with KMnO4, and then further into RGO/MnO2 composites by means of glucose-reduction. It is found that MnO2 nanoparticles with the size of 20–30 nm are uniformly distributed in the structure of RGO. A series of composites with different mass ratios of RGO to MnO2 has been proved superior catalytic activities, much higher than that of the bare MnO2 for decomposition of MB dye in the presence of H2O2. Typically, 50 mL of MB (50 mg L−1) can be completely decolorized and nearly 66% mineralized at 50 °C in 5 min with 10 mg of the RGO/MnO2 hybrid. According to the adsorption–oxidation–desorption mechanism, the high activity of RGO/MnO2 composites for decomposition of MB is closely related to the positive synergistic effect of RGO and MnO2 with the assistance of H2O2.