Polyaniline-modified carbon black supported platinum–cobalt alloy nanoparticle (Pt–Co/C-PANI) catalysts were prepared via a microwave-assisted polyol method and subsequent high temperature annealing. X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and derivative thermogravimetric (DTG) analysis were used to characterize the structure of the catalysts. We find that the electron delocalization between the metal d orbitals and PANI is beneficial for improving the ORR performance and the PANI on carbon can prevent the aggregation of Pt–Co nanoparticles during high temperature treatments. Electrochemical evaluations reveal that the obtained Pt–Co/C-PANI catalysts annealed at 500 °C show the highest mass activity of 1.33 A mg_Pt⁻¹ and a specific activity of 1.29 mA cm⁻², which are 7.8 and 5.4 times higher than those of the commercial JM Pt/C catalyst, respectively. X-ray photoelectron spectroscopy (XPS) results show that only part of PANI is decomposed at 500 °C and the metal–nitrogen (M–N) bonds are formed in Pt–Co/C-PANI-500 °C, which are attributed to the impressive ORR activity enhancement in Pt–Co/C-PANI-500 °C.