SnO2 thin2film gas2sensor was fabricated by sol2gel dip2coating process using SnCl2·2H2O as starting ma2terials. Temperature dependence characterristics of the resistance was investigated in four hazardous indoor gases(formaldehyde , benzene , dimethyl benzene , methyl benzene) . It was found that resistance2temperature characteristicswere different for different gases. Molecular orbital calculation results based on MOPAC indicate that resistance2tem2perature characteristics of SnO2 thin2film are related to the molecular orbital levels. Therefore measurement of resis2tance2temperature curves could enhance the selectivity of the SnO2 thin2film gas sensors.