Abstract We have investigated the interaction of Ag and S coadsorbed on a Ru(001) surface using high-resolution soft X-ray photoemission spectroscopy of the S 2p core level and valence region. The interaction of adsorbed sulfur and the first layer of Ag adatoms is weak. At ΘS + ΘAg < 0.5 ML, Ag and S are coadsorbed in segregated domains. The Ag layer is covered by chemisorbed S only after a S-saturation of the Ru surface (ΘS > 0.5 ML). At Ag coverages higher than one monolayer, the valence band and the S 2p spectra show formation of Silver sulfide at room temperature.