The hydrogen oxidation reaction (HOR) activity of PdRu bimetallic catalysts in acidic media is first investigated by preparing PdRu nanoparticles of various compositions (Pd:Ru atomic ratios of 1:0, 9:1, 3:1, 1:1, 1:9, 1:20 and 0:1) supported on carbon supports. Pd is under compressive strain when Pd and Ru atoms are alloyed, and PdRu(1:1) forms phase-separated nanoparticles. The crystallite size of PdRu/C can be reduced to ∼4 nm depending on the PdRu composition. While Ru/C shows a slightly faster HOR kinetics than Pd/C, the introduction of Ru to Pd improves the HOR kinetics leading to the highest kinetic current on PdRu9/C. The kinetic current and single-cell performance of PdRu9/C is comparable to those of commercial PtRu/C. First-principle calculations based on density functional theory indicate that the most stable position of the Pd atom is the 1st layer of the surface, which represents the possibility of surface segregation of Pd atoms. The theoretical calculations clearly unravel that the presence of strong electronic effect owing to Ru alloying with Pd, which would correspond to an optimum composition of PdRu9/C in the experiments, demonstrates a superior hydrogen oxidation activity to the other PdRu compositions. Display omitted •The hydrogen oxidation activity of PdRu/C in acidic media was first examined.•PdRu/C has a better hydrogen oxidation activity than Pd/C and Ru/C.•The single-cell performance of PdRu9/C is on the same level as commercial PtRu/C.•Theoretical calculations show both strain and ligand effects boost the activity.