Here, the hybrid of inverse spinel NiCo₂S₄ nanoparticles coated on activated carbon (AC) has been first described as an effective nonprecious electrocatalyst for oxygen reduction reaction (ORR) used in air cathode microbial fuel cells (MFCs). MFC with NiCo₂S₄/AC air cathode obtains the maximum power density of 2000 ± 59 mW/m², with a value of 125% higher than the control. The combination effect of mixed valence in NiCo₂S₄/AC composite is favorable for easier electron transfer to make O₂ absorbed and reduced. The intensity ratio of Raman D to G band (I_D/I_G) decreases from 0.85 (AC) to 0.78 (NiCo₂S₄/AC), indicating the formation of a partial graphite structure in NiCo₂S₄/AC.NiCo₂S₄/AC cathode shows better catalytic activity, lower internal resistance, higher kinetic activity and contains much octahedral catalytic active sites of Co³⁺, which favors a four electron ORR pathway. The finding shows NiCo₂S₄/AC will be a novel kind of promising nonprecious catalyst applied in MFC.