Al₂O₃was loaded with different amounts (5 wt%, 10 wt%, and 15 wt%) of Pd via isometric-impregnation. Transmission electron microscopy (TEM) demonstrated that the 15 wt% Pd/Al₂O₃has numerous Pd nanoparticles formed on Al₂O₃. To decrease the hydrolysis rate of Pd(NO₃)₂, which could cause the formation of Pd aggregates on Al₂O₃, determinate concentrations of HNO3 were mixed with the impregnation solution. The measuring results of TEM and Brunauer-Emmett-Teller-specific surface areas revealed that 15 wt% Pd loaded with 10 vol% HNO₃has high dispersion on Al₂O₃. The influences of the loading amounts of Pd and the acidity of the impregnated solution on the sensitivity and stability of gas sensors were investigated. Catalytic combustion gas sensors based on 15 wt% Pd/Al₂O₃prepared from a 10 vol% HNO₃-90 vork Pd(NO₃)₂impregnating solution exhibited high responses to methane and strong ability to resist organic silicon.