In this paper, the hybrid catalysts of manganese oxide decorated by silver nanoparticles (Ag-MnOx) are fully investigated and show the excellent oxygen reduction reaction (ORR) activity. The Ag-MnO2 is synthesized by a facile strategy of the electroless plating of silver on the manganese oxide. The catalysts are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Then, the ORR activities of the catalysts are systematically investigated by the rotating disk electrode (RDE) and aluminum-air battery technologies. The Ag nanoparticles with the diameters at about 10nm are anchored on the surface of α-MnO2 and a strong interaction between Ag and MnO2 components in the hybrid catalyst are confirmed. The electrochemical tests show that the activity and stability of the 50%Ag-MnO2 composite catalyst (the mass ratio of Ag/MnO2 is 1:1) toward ORR are greatly enhanced comparing with single Ag or MnO2 catalyst. Moreover, the peak power density of the aluminum-air battery with 50%Ag-MnO2 can reach 204 mWcm−2.