Developing low-cost non-precious metal catalysts for high-performance oxygen reduction reaction (ORR) is highly desirable. Here a facile, in situ template synthesis of a MnO-containing mesoporous nitrogen-doped carbon (m-N-C) nanocomposite and its high electrocatalytic activity for a four-electron ORR in alkaline solution are reported. The synthesis of the MnO-m-N-C nanocomposite involves one-pot hydrothermal synthesis of Mn3O4@polyaniline core/shell nanoparticles from a mixture containing aniline, Mn(NO3)(2), and KMnO4, followed by heat treatment to produce N-doped ultrathin graphitic carbon coated MnO hybrids and partial acid leaching of MnO. The as-prepared MnO-m-N-C composite catalyst exhibits high electrocatalytic activity and dominant four-electron oxygen reduction pathway in 0.1 M KOH aqueous solution due to the synergetic effect between MnO and m-N-C. The pristine MnO shows little electrocatalytic activity and m-N-C alone exhibits a dominant two-electron process for ORR. The MnO-m-N-C composite catalyst also exhibits superior stability and methanol tolerance to a commercial Pt/C catalyst, making the composite a promising cathode catalyst for alkaline methanol fuel cell applications. The synergetic effect between MnO and N-doped carbon described provides a new route to design advanced catalysts for energy conversion.