Abstract: Highly thermostable palladium catalysts have been prepared by sol-gel method. The possible effects of pH of alumina gel precursor on the final structure and thermal stability of catalyst have been investigated by the wide-angle X-ray diffraction, laser light scattering (LLS) and BET techniques. The results indicated that pore size distributions of catalyst are related with the gel particle size distributions, which were strongly dependent on the pH of the system. It was found that the Pd particles could be anchored within the relatively stable alumina host structure by sol-gel method and resulted in elevation of hydrothermal stability, as well as the enhancement of catalytic activity for CO and C3H6 oxidation over aged catalysts. In addition, it was found that the La2O3 additive could elevate the phase transfer temperature of alumina remarkably, whereas it promoted the sintering of Pd to form bigger particle size at high temperature. The experimental results showed the La2O3 additive could promote the catalytic activities for oxidation of CO and C3H6 over fresh Pd catalysts. However, the activities were a little lower than that of unmodified catalyst after aged at 1050 ℃ for 24 h due to more serious sintering of Pd metal on the surface.