Abstract: The preparation method of gas sensitive material SnO₂ obtained by adding ammonia water to SnCl₄ aqueous solution is studied. The XRD spectrum of the SnO₂ which is calcined for 2 hours at 500℃ and then aged at 300℃, is similar to that of the SnO₂ which is calcined at 700℃, but the special surface of the former is 10 m²/g more than the latter, the proportion of the former to the latter is 0.69. According to this, the R₀ ratio of the two is 0.66. (R₀ is the stable rsistance in clean air at 250℃) and the R_g ratio of the two is 0.665(R_g is the Stable resistance in ethanol-air (of 500×10^-6 vol. ratio) at 250℃). The sensitivity of the former to ethanol vapor is a little better than the that of latter, and the formler is slightly suitable for gas sensitive material.