MnO2 has been demonstrated to be an effective catalyst for Zn-air batteries, but suffers from cripplingly low cell performance due to its limited electrical conductivity. In this work, we report a facile process for preparing the MnO2/C air cathode by directly anchoring the MnO2 onto Ketjen Black (KB) via an in-situ redox reaction. It is demonstrated that a Zn-air battery installed with the proposed MnO2/KB air cathode outperforms that installed with a commercial Pt/C cathode. Specifically, the MnO2/KB cathode presents a more positive ORR onset potential and a larger current density compared with that of the Pt/C cathode. Under ambient air, the prepared MnO2/KB air cathode allows the battery to reach a peak power density of 133.17mWcm−2 when operated at a current density of 188.51mAcm−2, which is among the highest values in the literature. More impressively, the battery installed with the proposed cathode can be operated at a high current density of up to 100mAcm−2 with a voltage discharge plateau larger than 1.0V. These results indicate that the MnO2/KB electrode offers a promising option for both alkaline fuel cells and metal-air batteries.