By one-step pyrolysis of a unique "cage-in-cage" cobalt metal-organic framework, nitrogen-doped carbon cubes embedded with numerous metallic Co nanoparticles were obtained. A considerable amount of Co particles was encapsulated in thin carbon shells and formed the core-shell-like Co@C structure. With about 60 wt% Co particles in the prepared sample, the nanocomposites of Co nanoparticles and nitrogen-doped carbon show electrocatalytic activity for the oxygen reduction reaction (ORR) with an efficiency comparable to the commercial Pt/C catalyst, but with better durability and methanol-tolerance performance. The metallic Co nanoparticles were found to play an important role in enhancing the ORR activity of the nanocomposites. This simple one-step pyrolysis method provides a novel synthetic route for the synthesis of core-shell-like Co@C nano-composites. The synthesized material represents a highly active non-precious metal catalyst for ORR.