Abstract: Using SnO₂-ZrO₂ and SnO₂-ThO₂ systems as the gas sensitive materials, we have investigated the effects of sintering temperature on the structure and particle size as well as on the sensitivities and selectivities of the material. The experimental results show that the sintering temperature not only effects on the sensitivity of gas sensitive materials but also strongly on their selectivity under the experimental conditions.The sensitivity of the material does not always decrease as sintering temperature increases,it sometimes gives a maximum value at certain temperature of sintering and for SnO₂-ZrO₂ system its selectivity loses when sintering temperature is elevated up to 800℃.