Nano crystalline SnO2 was prepared by sol-gel with PEG surfactant. CuO was doped in the SnO2 by mechanical mixture and reaction congelation from CuCl. The samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen adsorption isotherms (BET). The results indicated that the average crystal size of SnO2 at sintering temperature of 550 °C was 10 nm, the conglomeration size of SnO2 was about 100 nm. The specific surface area of pure SnO2, mechanical doping SnO2 and reaction doping SnO2 were 110, 84, 72 m2/g, respectively. The thick film gas sensors made from these samples were examined. SnO2 doped by different methods had different electrical and gas-sensing properties. The sensors based on CuO doped SnO2 films exhibited less sensitive to ethanol gas but extremely higher sensitivity to H2S gas than that of pure SnO2.