Promoting the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics of cathode catalysts is significant to improve the discharge/charge performance of Li-O-2 batteries (LOBs). To develop high-performance advanced electrocatalysts, porous perovskite La0.9Mn0.6Ni0.4O3-delta (LMN) nanofibers with in situ exsolved Ni nanoparticles have been synthesized by the electrospinning method, followed by reduction under a 5% H-2/Ar atmosphere. The results confirm that due to the numerous in situ exsolved Ni nanoparticles and oxygen vacancies formed on the surface of LMN nanofibers, the electronic conductivity, active site distribution, and O-2 adsorption of the cathode are dramatically improved. Furthermore, the Ni nanoparticles and oxygen vacancies generated on the surface of the LMN perovskite have enhanced the ORR/OER activities effectively. LOBs with the Ni-LMN cathode can deliver an impressive discharge capacity of 16 656 mAh g(-1) and long-term stability of about 95 cycles at a current density of 400 mA g(-1). These results reveal an exciting opportunity to develop a multifunctional perovskite for the high-performance LOBs.