Carbon nanotube-supported bimetallic Pd nanoparticles (NPs) with atomic Pt cluster surface decoration (the mole ratio of Pt/Pd is 0.1) are synthesized by a wet chemical method with sodium borohydride as the reducing agent. The core component is controlled by metal ion reduction sequences. The mass activity for the oxygen reduction reaction (ORR) over Pt metal of the presented PdPt NPs is improved by 29.4 times as compared to that of commercial Pt catalysts. Such an enhancement is accounted by an expanded Pt–Pd bond length and heteroatomic intermixing-induced electron relocation.