The ability for tuning not only the composition but also the type of surface facets of alloyed nanomaterials is important for the design of catalysts with enhanced activity and stability through optimizing both ensemble and ligand effects. Herein we report the first example of ultrathin platinum-gold alloy nanowires (PtAu NWs) featuring composition-tunable and (111) facet-dominant surface characteristics, and the electrocatalytic enhancement for the oxygen reduction reaction (ORR). PtAu NWs of different bimetallic compositions synthesized by a single-phase and surfactant-free method are shown to display an alloyed, parallel-bundled structure in which the individual nanowires exhibit Boerdijk-Coxeter helix type morphology predominant in (111) facets. Results have revealed intriguing catalytic correlation with the binary composition, exhibiting an activity maximum at a Pt:Au ratio of similar to 3:1. As revealed by high-energy synchrotron X-ray diffraction and atomic pair distribution function analysis, NWs of this ratio exhibit a clear shrinkage in interatomic bonding distances. In comparison with PtAu nanoparticles of a similar composition and degree of shrinking of atomic-pair distances, the PtAu NWs display a remarkably higher electrocatalytic activity and stability. The outperformance of NWs over nanoparticles is attributed to the predominant (111)-type facets on the surface balancing the contribution of ensemble and ligand effects, in addition to the composition synergy due to optimal adsorption energies for molecular and atomic oxygen species on the surface as supported by DFT computation of models of the catalysts. The findings open up a new pathway to the design and engineering of alloy nanocatalysts with enhanced activity and durability.