TiO2-ZrO2 composite oxides with a series of different Ti/Zr atomic ratios were synthesized by using a deposition precipitation method and employed as supports to prepare Ru catalysts. The physicochemical characteristics of Ru catalysts were tested by N-2 adsorption, CO chemisorption, X-ray diffraction, H-2 temperature-programmed reduction, scanning electron microscopy, transmission electron microscopy, NH3 adsorption, and X-ray photoelectron spectroscopy, and their catalytic hydrodeoxygenation (HDO) performance was evaluated by using guaiacol as a model compound. The Ru/TiO2 catalyst exhibits low HDO activity due to the surface modification of Ru particles with Ti3+ species formed during the reduction of Ru/TiO2. The HDO activity of Ru catalysts was significantly promoted by ZrO2 in the supports because it can hinder the migration of Ti3+ species onto the surface of Ru particles and thus more Ru active sites are exposed. The higher selectivity of benzene for Ru catalysts supported on TiO2-ZrO2 composite oxides suggests that they are promising supports for Ru catalysts in the HDO reaction of guaiacol.