Gas sensors have been fabricated using the single-crystalline ${\mathrm{SnO}}_2$ nanobelts. Electrical characterization showed that the contacts were ohmic and the nanobelts were sensitive to environmental polluting species like CO and ${\mathrm{NO}}_2,$ as well as to ethanol for breath analyzers and food control applications. The sensor response, defined as the relative variation in conductance due to the introduction of the gas, is 4160% for 250 ppm of ethanol and $\text{−1550\%}$ for 0.5 ppm ${\mathrm{NO}}_2$ at $\text{400\hspace{0.05em}°}\mathrm{C}.$ The results demonstrate the potential of fabricating nanosized sensors using the integrity of a single nanobelt with a sensitivity at the level of a few ppb.