Non-precious iron-nitrogen doped carbon material (Fe-N/C) is the most promising candidate to replace platinum-based catalysts for oxygen reduction reaction (ORR) taking place at the cathode in fuel cells. In this study, three-dimensionally (3D) ordered mesoporous Fe-N/C with open porous structure is successfully synthesized. The obtained shape is a rhombic dodecahedron which corresponds to a single mesoporous crystal with body-centered cubic structure (Im-3m). By applying an optimal post-treatment of NH3 activation, a high content of beneficial pyridinic nitrogen can be doped while maintaining the ordered mesoporous architecture with high surface area and large pore volume. Our mesoporous Fe-N/C greatly promotes ORR performance with a high onset potential of 1.018 V and limited-diffusion current density of 5.98 mA cm¿2 in alkaline electrolyte. Interestingly, this mesoporous Fe-N/C also shows good ORR catalytic activity in acidic condition with onset potential and limited-diffusion current density as high as 0.935 V and 5.60 mA cm-2, respectively.