Titanium dioxide (TiO2-anatase phase) thin films, consisting of agglomerated, flower-like nanoparticles, have been synthesized using an ultrasonic spray pyrolysis (USP) method in combination with titanium (IV) oxide acetylacetonate [TiO(acac)2] and methanol at 550°C. These thin films were subsequently thermally treated in air at 950°C for 6 h, and the flower-like particles were transformed into smooth surfaces mainly comprising the TiO2-rutile phase. In order to prepare oxygen sensors, TiO2 thin films were deposited on interdigitated gold electrodes in contact with alumina substrates. The silver colloidal solution was impregnated on the TiO2 thin film. Since the solvent in which the silver nanoparticles are suspended evaporates at 200°C, the thin films were then annealed at this temperature in air for 1 h. The effect of colloidal silver nanoparticles on the response of the thin-film TiO2 oxygen sensors was studied in a mixture with zero-grade air. The gas-sensing properties of TiO2 sensors in an atmosphere of 104 ppm oxygen were measured between 25 and 500°C. The experimental results obtained with colloidal silver nanoparticles as surface additives show that the sensitivity reaches constant values for the TiO2-anatase and TiO2-rutile phases of 0.40 and 0.03, respectively, at an O2 concentration of 100 ppm in zero-grade air at 300°C, which is as high as the values reported for oxygen sensors prepared by more expensive techniques.