Transition metal- and N-codoped carbon nanotubes (CNTs) have superior catalytic activity because the curling surface enhances the bonding ability of atoms within CNTs to other species. However, it is a great challenge to prepare CNTs with transition metal- and N-doped at high level during the growth of CNTs. Here, (Fe,N-codoped CNT)/(Fe-based nanoparticle) (Fe,N-CNT/FeNP) hybrid nanostructures are for the first time prepared through the carbonization of Fe-doped g-C3N4. The doping of Fe and N is simultaneously realized during the formation of CNTs. Meanwhile, the abundant and homogeneous Fe and N in Fe-doped g-C3N4 ensure high-level and uniform doping of Fe and N in CNTs. The Fe,N-CNT/FeNP hybrid nanostructures have several types of active components, including homogeneously distributed coordinating Fe moieties (FeCxNy or FeNx) and CFe15.1 nanoparticles embedded in Fe,N-CNTs, towards oxygen reduction reaction (ORR). A superior ORR electrocatalytic performance is therefore obtained on the Fe, N-CNT/FeNP nanohybrids. Our preparation method opens an avenue to preparation of CNTs with transition metal- and N-doping at high-level, and the superior performance of Fe,N-CNT/FeNP nanostructures for ORR will be very helpful to the development of fuel cells and metal-air batteries. (C) 2020 Elsevier Inc. All rights reserved.