The development of cost-effectiveness and efficient bifunctional electrocatalysts is essential for the commercialization of rechargeable metal-air batteries. Herein, a controlled one-step alginate biomass carbonization strategy is presented to prepare the FeCox alloy nanoparticles encapsulated in N-doped porous carbon/multiwalled carbon nanotubes composites (FCx-NC/CNTs). Benefiting from the particular core-shell structure, high dispersion of active sites (FeCox alloy nanoparticles) and fine conductive network (CNTs and N-doped porous carbon), the optimized FCx-NC/CNTs-10 (containing 10 wt% CNTs in FCx-NC/CNTs) hybrid displays a remarkable bifunctional activity and long-term stability for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Notably, the corresponding bifunctional activity parameter (ΔE) is as low as 0.80 V, outperforming most state-of-the-art reported bifunctional electrocatalysts. Moreover, the FCx-NC/CNTs-10 based rechargeable Zn-air battery exhibits a fast dynamic response and an excellent rechargeability with a high peak power density of 156 mW cm−2 and a narrow voltage loss after continuous operating 430 cycles (∼144 h). This kind of FCx-NC/CNTs hybrid with excellent electrochemical catalytic activity provides a great potential in metal-air batteries.