The pellet-type SnO2 sensor was synthesized by the solid state method and the effects of additives such as nano ZnO (1-12 mol %) and nano In2O3 (1-10 mol %) on the CO gas sensitivity of sensor were investigated. The optimum sintering temperature was chosen 800°C because of the porosity content of the samples. The phase analysis and microstructure of the samples were studied by x-ray diffraction and scanning electron microscopy, respectively. Results show that the electrical resistivity

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... s of the samples with time increased by increasing the amount of additives up to the optimum value for each additive. These optimum values were 10 and 7.5mol% for nano ZnO and nano In2O3, respectively. The best sensitivity and recovery and response times were obtained in the co-doped sample containing 10 mol% nano ZnO and 7.5 mol% nano In2O3. The higher values of the additives decreased the sensitivity of the samples due to the formation of undesirable phases.