The effect on the heat resistance of the catalysts has been studied upon the addition of cerium to basic three way catalyst(PtRh/Al2O3) and of alkaline earth/rare earth metal to the standard three way catalyst(PtRh-Ce/Al2O3). Light-off temperature and three way conversion rate were evaluated with the simulated automotive exhaust gas mixture of H2, CO, C3H6, C3H8, NO, CO2, O2, H2O and N2 over fresh catalyst and over the aged one at 950℃ for 100 hours. The prepared catalysts were characterized utilizing BET and SEM. The addition of cerium to the PtRh/Al2O3 catalyst severely reduced the oxidation of CO and hydrocarbon under the lean condition(λ=1.03) and the reduction of NO(x) under the rich(λ=0.97) or stoichiometric condition(λ=1.00) due to sintering of cerium with the precious metals and producing of CeAlO 3 compound with alumina. When alkaline earth(Mg, Ca, Sr or Ba) or rare earth metal(La or Nd) was added to PtRh-Ce/Al2O3 and aged, catalyst with barium showed the highest catalytic activity with the best thermal stability, and neodymium, strontium and lanthanum added catalysts had the higher activities in the order. However, calcium addition to the catalyst had little effect on the thermal stability, showing a little higher catalytic activity with the standard catalyst. Magnesium added catalyst was extremely deactivated compared to the standard catalyst due to the enhanced sintering with precious metal and alumina.