Despite the recent advances in preparing high-efficiency and durable electrocatalysts for oxygen reduction reaction (ORR) toward fuel cell applications, there is still lacking of the understanding regarding the relationship between the electrocatalytic performance and the surface structure of the catalyst at atomic level. Herein, three PdZn bimetallic composites named as PdZn_Disordered, PdZn_Ordered and Pd@Zn_Core-shell (Pd: Zn =1: 1) were prepared for ORR in alkaline medium to examine the surface structure effects. Multiple characterization means revealed that PdZn_Disordered and PdZn_Ordered had amorphous PdZn and ordered PdZn alloyed structure, respectively, while Pd@Zn_Core-shell held a Pd core-ordered and Zn-shell-disordered architecture. In the electrochemical ORR tests, Pd@Zn_Core-shell exhibited the superior activity and stability in the series, outperforming the Pd/C and Pt/C catalysts. The electrocatalytic performance followed the order of Pd@Zn_Core-shell > PdZn_Ordered n PdZn_Disordered, which can be attributed to the effects of different surface structures of the catalysts. (C) 2019 Elsevier Inc. All rights reserved.