SnO<sub>2sub>-core/In<sub>2sub>O<sub>3sub>-shell nanobelts were fabricated by a two-step process comprising thermal evaporation of Sn powders and sputter-deposition of In<sub>2sub>O<sub>3sub>. Transmission electron microscopy and X-ray diffraction analyses revealed that the core of a typical core-shell nanobelt comprised a simple tetragonal-structured single crystal SnO<sub>2sub> and that the shell comprised an amorphous In<sub>2sub>O<sub>3sub>. Multiple networked SnO<sub>2sub>-core/In<sub>2sub>O<sub>3sub>-shell nanobelt sensors showed the response of 5.35%at a NO<sub>2sub> concentration of 10聽ppm at 300聽掳C. This response value is more than three times larger than that of bare-SnO<sub>2sub> nanobelt sensors at the same NO<sub>2sub> concentration. The enhancement in the sensitivity of SnO<sub>2sub> nanobelts to NO<sub>2sub> gas by sheathing the nanobelts with In<sub>2sub>O<sub>3sub> can be accounted for by the modulation of electron transport by the In<sub>2sub>O<sub>3sub>-In<sub>2sub>O<sub>3sub> homojunction.