In this work, porous MnO/C composites were successfully synthesized via a new ammonia diffusion method, in which the MnO nanoparticles were tightly embedded into a porous carbon matrix. Kapok fibers (KFs) were used as both the bio-template and the renewable carbon source. The KFs-templated MnO/C electrodes exhibited a high reversible specific capacity of 1454mAhg−1 with a high coulombic efficiency, up to 98%, at a current density of 200mAg−1 over 150 cycles. The high reversible capacity of the MnO/C composites could be ascribed to the synergetic effects of several factors including the unique porous microstructure, the small MnO nanoparticle size and the high defective carbon matrix. Due to the small MnO nanoparticles size and a moderate amount of carbon (13.3wt%), the electrodes showed a small voltage polarization (about 0.89V).