The adsorption and desorption of water on the surfaces of ruthenium catalysts have been studied using the techniques of uptake, thermal desorption spectroscopy（TDS）, Auger electron spectroscopy(AES), and low-energy electron diffraction(LEED) under ultrahigh vacuum conditions. Water adsorbs molecularly at room temperature giving a desorption peak at 380 K and a saturation coverage of less than a thousandth of a monolayer. At higher temperatures water dissociates leaving oxygen adatom, O(a), and the maximum dissociation rate is observed at 480 K. The dissociated surface oxygen is evidenced to penetrate into the subsurface and/or the bulk.