An efficient oxygen reduction reaction (ORR) on the air cathode is a prerequisite for high-performance metal-air batteries (MABs), as it decreases the excessive charge-discharge overpotential to reduce side-reactions. Here, we develop a composite catalyst for MABs by loading ultrathin CeO2 nanoflakes (UCNFs) on a three-dimensional graphene (3DG) network to form the UCNFs@3DG. The UCNFs@3DG composite features a high activity approaching the commercial Pt/C catalyst in the ORR, probably due to synergic effects of the catalytically active UCNFs and the conductive 3DG network. The UCNFs@3DG can serve as an efficient air cathode in a series of MABs, delivering a capacity of 613 mAh h gZn −1 in the Zn-air battery (ZAB) and 839 mAh h gAl −1 in the Al-air battery (AAB), respectively. Finally, the UCNFs@3DG cathode in lithium-oxygen batteries (LOBs) achieves a high discharge capacity of 21,166 mAh h gc −1 at 0.2 A gc −1 and over 15,000 mAh h gc −1 under elevated current densities up to 2 A gc −1, validating the UCNFs@3DG as a general air cathode in MABs.