Despite the fact that both electrochemical experiments and density functional theory calculations have testified to the superior electrocatalytic activity and CO-poisoning tolerance of platinum–ruthenium (PtRu) alloy nanoparticles toward the methanol oxidation reaction (MOR), the facet-dependent electrocatalytic properties of PtRu nanoparticles are scarcely revealed because it is extremely difficult to synthesize well-defined facets-enclosed PtRu nanocrystals. Herein, we for the first time report a general synthesis of ultrathin PtRu nanocrystals with tunable morphologies (nanowires, nanorods, and nanocubes) through a one-step solvothermal approach and a systematic investigation of the structure-directing effects of different surfactants and the formation mechanism by control experiments and time-dependent studies. In addition, we utilize these {100} and {111} facets-enclosed PtRu nanocrystals as model catalysts to evaluate the electrocatalytic characteristics of the MOR on different facets. Remarkably, {111}-terminated PtRu nanowires exhibit much higher stability and electrocatalytic mass activity toward MOR, which are 2.28 and 4.32 times higher than those of {100}-terminated PtRu nanocubes and commercial Pt/C, respectively, indicating that PtRu {111} facets possess superior methanol oxidation activity and CO-poisoning resistance relative to {100} facets. Our present work provides a series of well-defined PtRu nanocrystals with tunable facets which would be ideal model electrocatalysts for fundamental research in fuel cell electrocatalysis.