•A CoFe2O4@N-AC nanohybrid was successfully in suit synthesized.•CoFe2O4@N-AC nanocomposite served as electrocatalyst for the air cathode of MFCs.•The rate and kinetics constant for oxygen reduction reaction were greatly enhanced.•The MPD of CoFe2O4@N-AC was 1770.8±15.0mWm−2, 2.39 times higher than the control AC.•CoFe2O4@N-AC nanocomposite is a potential electrocatalyst for air-cathode MFCs. Cathodic catalysts play a key role in the enhanced performance of microbial fuel cells (MFCs), and exploring low cost and highly active catalysts is greatly important for the future development of MFCs. Herein, spinel CoFe2O4 (CFO) nanoparticles (NPs) were successfully in situ generated onto nitrogen-doped activated carbon by a hydrothermal-assisted annealing assembly method. The synergistic effect between CFO and N-AC in the CFO@N-AC nanocomposites take advantages of a large surface area, the less total resistance, fast electron transport and the excellent electrocatalytical activity for oxygen reduction reaction (ORR) from both the N-AC and CFO. The mechanism of oxygen reduction for CFO@N-AC catalyst is a direct four-electron pathway. The as-acquired CFO@N-AC nanocomposites serve as the air-cathode catalyst in single chamber MFCs. The performance of MFCs is markedly enhanced utilizing the CFO@N-AC material, with the maximum power density measured to be 1770.8±15.0mWm−2, which is 2.39 times higher than that of the control AC. The superior catalytic performance make the low-cost CFO@N-AC possess a promising outlook for the practical application of MFCs.