SnO2 thin films having low resistivity were prepared by chemical vapor deposition. Conductivity, its dependence on temperature, and Hall effect of films were measured. Examination of the surface morphology by scanning electron microscope showed that the SnO2 thin films are made up of many grains. Experimental results were discussed by the grain-boundary model. The carrier transport mechanism across a grain boundary is the tunnel effect rather than the thermionic emission.