Core/shell nanocatalysts have been regarded as potential catalysts for oxygen reduction reaction (ORR) occurring at the cathode of proton exchange membrane fuel cells. Notably, core/shell segregated nanocatalysts exhibit improved activity and stability compared with alloyed nanocatalysts because of the high noble metal utilization and electronic modification effect. Herein, we report that the ORR activity and stability of PtAuSn core/shell ternary nanorod catalysts are fine-structure-dependent in which AuSnOx-decorated Pt catalysts can reach a high ORR mass activity of 1069 mA/mgPt at 0.85 V (IR-free). Moreover, the Au@SnOx-decorated Pt catalysts with a surface SnOx protective layer show high ORR stability after an accelerated durability test of 10,000 cycles, which yet maintain a high mass activity (251 mA/mgPt). This research highlights that controlling the fine structure of catalysts can effectively promote the activity and durability of the electrocatalysts for fuel cells.