The interfaces of multicomponent hybrid nanoparticles (MHNPs) have great effects on their electrocatalytic activities. Herein, a highly active multifunctional catalyst heterostructure PdO-doped Co3O4 (PdCo-300) nanoparticles with closely mutually connected interfaces were synthesized by a convenient strategy. The prepared PdCo-300 nanoparticles displayed high catalytic activities for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline media. The results show that the considerable electrocatalytic activities and stabilities are associated with the formation of MHNPs with intimate connected boundary between PdO and Co3O4. At the interface, the decrease of Pd electron density (downshift of the D-band center) and the formation of large amount of oxygen vacancies in Co3O4 promoted the electrocatalytic performance. Theoretical calculations show that the synergy of Pd ions and Co ions at the interface can enhance the interaction between active oxygen species and the catalyst surface, resulting in the decrease of energy barrier for ORR.