Magnesium-air fuel cells are considered as a potential energy conversion device owing to a high theoretical specific capability, economic viability and environmental friendliness. In this work, alpha-MnO2 nanorods are supported on three-dimensional graphene (3D-G) which is fabricated with coal tar pitch as the carbon precursor and MgO as the template via hydrothermal reaction. The synergistic interactions between alpha-MnO2 nanorods and 3D-G improve the activity and durability performance for oxygen reduction reaction in 0.1 mol L-1 KOH solution. alpha-MnO2/3D-G exhibits a high half-wave potential (0.81 V) and superior to alpha-MnO2/C (0.72 V) and alpha-MnO2/rGO (0.76 V), and close to 20 wt% PVC (0.83 V). alpha-MnO2/3D-G also possesses higher durability than commercial PVC. Furthermore, the magnesium-air fuel cells based on alpha-MnO2/3D-G, air-cathode display the peak power density (106.2 mW cm(-2)), and continuously durability (discharge for 16 h at 50 mA cm(-2) with the mere decay of cell voltage by 7.6%). These results prove that alpha-MnO2 /3D-G catalyst with high activity and durability can be a promising electrocatalyst in magnesium-air fuel cells.