X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) are employed for a comparative study of the surface composition and electronic structure of an Au/TiO$_{2}$ catalyst in the asprepared state and after using it in the reaction of CO oxidation at room temperature. As found, the reaction-induced changes in the morphology of Au nanoparticles related to their agglomeration are accompanied by modification of the electronic state of the catalyst via an enhanced electron transfer to the gold atoms that shows up as an additional negative shift of the Au 4f spectrum and its distortion. The catalytic reaction of CO oxidation results in the loss of hydroxyl groups and accumulation on the support surface of various carbon-containing species with the leading formation of carbonate and bicarbonate groups, which increases with time on stream. The role of these factors in deactivation of the catalyst is discussed.