Objective To prepare a Pt/ C@ PANI core-shell catalyst with high catalytic activity and durability. Methods The polyaniline (PANI)-decorated Pt / C@ PANI core-shell catalyst was prepared by in situ chemical oxidation polymerization method. The stability and activity of the Pt / C@ PANI catalyst prepared were evaluated using accelerated durability test (ADT), along with the monitoring of electrochemical surface area ( ECSA), oxygen reduction reaction ( ORR) activities, X-ray photoelectron spectrometer (XPS) and transmission electron microscopy (TEM), and the density functional theory (DFT) calculations were carried out to investigate the essential reasons for the enhanced catalytic activity and durability of Pt / C catalyst by PANI. Results The experimental results demonstrated that the activity for the ORR strongly depended on the PANI content and the thickness of the PANI shell, and that the prepared Pt / C@ PANI(30% ) catalyst with 5 nm PANI exhibited a Pt mass and a specific activity of nearly 1. 6 and 1. 8 times higher than those of the commercial Pt / C catalysts. The accelerated stability test showed that the ECSA of Pt / C@ PANI(30% ) catalyst was only decreased by ~ 30% , whereas the Pt / C catalysts lost ~ 83% of the initial ECSA after 1500 cycles of CV scanning. The DFT calculations disclosed that the number of holes in PANI increased with the electrons transfer from PANI to the supporting C, which caused partial oxidation of PANI and thus strengthened the electric conductivity of PANI. The lifted HOMO energy level and lowered d band center of Pt / C@ PANI compared with Pt / C were beneficial to the electron transfer between Pt / C@ PANI and O2 due to the reduced gap between the Pt / C@ PANI HOMO and the oxygen LUMO, and the desorption of intermediate species on the surface of the catalysts and releasing fresh catalytic sites for the subsequent reaction. Conclusion The PANI-decorated layer could enhance the Pt-support interaction and help to inhibit Pt dissolution / re-deposition, aggregation and ripening, which effectively solve the problem of Ostwald enlargement of the Pt / C catalyst, resulting in significant enhancement in the activity and stability of the catalyst.