The gas-sensitivity properties of SnO2 thin films as well as Ag/SnO2 and SnO2/Ag structures in an atmosphere containing propane (C3H8) were examined. The SnO2 and Ag films were deposited by a spray pyrolysis technique and vacuum evaporation, respectively. Soda-lime glass was used as the substrate for all the structures in this study. The sensors were measured in a propane atmosphere with different gas concentrations (50, 100, 200, 300, 400, and 500 ppm) at different operation temperatures (22, 100, 200, and 300 °C). The Ag/SnO2 structure, sintered a 400 °C for 1 h, showed the highest sensitivity, of the order of 400 at an operation temperature of 200 °C. The results show that the addition of Ag in the tin oxide films effectively acts as a catalyst in propane sensors and confirm the potential feasibility of using Ag as a catalyst in SnO2-based propane sensors.