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A heterogeneous nanocomposite of Fe–Fe3C nanoparticles and Fe–Nx sites on N-doped porous carbon allows for efficient synthesis of quinolines and quinazolinones via oxidative coupling of amines and aldehydes in aq. solution using H2O2 as the oxidant., In this paper, we developed a reusable heterogeneous non-precious iron nanocomposite comprising metallic Fe–Fe3C nanoparticles and Fe–Nx sites on N-doped porous carbon, which allows for highly efficient synthesis of quinolines and quinazolinones via oxidative coupling of amines and aldehydes using H2O2 as the oxidant in aqueous solution under mild conditions. A set of quinazolines and quinazolinones were synthesized in high yields with a broad substrate scope and good tolerance of functional groups. Characterization and control experiments disclose that a synergistic effect between the metallic Fe nanoparticles and built-in Fe–Nx sites is primarily responsible for the outstanding catalytic performance. Furthermore, the iron nanocomposite could be readily recovered for successive use without appreciable loss in catalytic activity and selectivity. This work provides an expedient and sustainable method to access pharmaceutically relevant N-heterocycles.