In this work, a high-performance composite catalyst comprised of IrO2 nanoparticles mounted on Co and N co-doped reduced graphene oxide (Co-N-rGO) is designed and successfully prepared for use in a Li-O2 battery. A battery with this catalyst as the cathode demonstrates very high capacity retention ability and cycling stability: it delivered a high reversible capacity of 11,731mAhg−1 after five cycles at 200mAg−1, and after 200 cycles with limited capacity of 600mAhg−1, the battery’s discharge terminal voltage remains over 2V and its energy efficiency still above 65%. Doping with Co and N, along with mounting the IrO2 nanoparticles, greatly enhances the catalyst’s performance. We suggest that its outstanding performance is attributable to the high surface area of rGO, the enhanced oxygen reduction reaction (ORR) activity arising from doping with Co and N, and the high dispersion and great promotion of IrO2 nanoparticles.