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Carbon materials have been used as negative electrodes for supercapacitor applications; nevertheless, owing to the low capacitance, they have limited ability to enhance the supercapacitor electrochemical properties. Here, we employ a facile chemical precipitation method for preparing a squirrel cage structure Fe 3 O 4 @carbon nanocomposite. In this architecture, the carbonized crosslinked bovine serum albumin (C) will play critical roles, serving as a skeleton for the deposition of Fe 3 O 4 and a transportation pathway like "high-speed rail" for electrons, maintaining the structural stability as well as accommodating the volume expansion of Fe 3 O 4 and facilitating electron transportation and the electrolyte ion diffusion. The iron oxide nanoparticles (Fe 3 O 4 ) exhibit superior reversible redox characteristics, hence increasing the supercapacitor performance. Benefiting from a stable structure, an aqueous asymmetric supercapacitor using a CNT@Ni(OH) 2 positive electrode (cathode) and Fe 3 O 4 @C negative electrode (anode) has also been assembled, which presents a high energy density of 17.3 W h kg -1 at a power density of 700 W kg -1 . The strategy for choice of Fe 3 O 4 @C composites will provide new opportunities for future supercapacitors with superior cyclability and high power density., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)