Spontaneous deposition of Pt on a Ru(0001) single crystal surface has been demonstrated by in situ scanning tunneling microscopy and linear sweep voltammetry techniques. The immersion of a ultra-high vacuum (UHV) prepared Ru single crystal in a platinum-ion-containing solution results in the formation of monolayer-to-multilayer Pt deposits without application of an external potential. The coverage and morphology of the Pt deposit depend on the concentration of platinum ions and the time of immersion. This simple method can be applied to Pt deposition on Ru nanoparticles, which can considerably reduce Pt loading in Pt/Ru electrocatalysts. The electrochemical behavior of such Pt/Ru(0001) bimetallic surfaces depends on the coverage of the Ru electrode and amount and morphology of the Pt deposit, which indicates a pronounced electronic modification of the Pt adlayer due to a strong Pt/Ru interaction.