Developing highly active and stable nanocarbon electrocatalysts for the oxygen reduction reaction (ORR) in alkaline medium has attracted much attention due to their potential as an alternative to traditional metal-based or noble metal catalysts. Herein, a unique micro-nano structure of (B, N)-rich B-C-N nanosheet-assembled microwires (BCNNAM) were synthesized and driven electrochemical oxide reduction reaction. The diameter of the microwires about 1 mu m, while the nanosheets have an average thickness of less than 20 nm. The compact nanosheets are mostly separated with a bending, curling and crumpling morphology. All those constitutes a ternary system with large surface area and abundant activity sites facilitate fast mass/electron transport for ORR catalytic activity. Thus, the B, N-rich B-C-N nanosheet-assembled microwires show significantly improved electrocatalytic activity with an onset potential of 0.95 V and half-wave potential of 0.83 V compared to BNNAM, nitride-doped carbon, porous carbon and a commercial Pt/C electrocatalyst. Such high catalytic performance of B, N-rich B-C-N micro-nano structures is due to the enhanced activity by the coexistence of B, C and N and the mass transfer promoted by the unique hierarchical porous structure. B, N-rich BCNNAM (nanosheet-assembled microwires), produced via a conbining growth mechanism of VLS and VS, showed excellent electrocatalytic performances for ORR due to synergistic effect arising from B, C and N as well as hierarchical porous structure.image