Highly dispersed SnO2 nanoparticels were synthesized at ambient conditions based on carbon microspheres, and the gas sensing properties of the material were studied systematically. The conductance responses of the material were measured by exposing it to ethanol gas (C2H5OH). It was found that the sensor exhibited better sensing responses to ethanol gas than the commercial SnO2 at the working temperature of 330 ℃. Furthermore, the gas sensor responses increased linearly with the increment of the gas concentrations of ethanol in the range from 5×106 to 200×106.