SnO2 nanosheets sensitized by ZnO quantum dots were used to fabricate UV excitation gas sensors for room temperature application. The morphology and structure of the as-synthesized samples were characterized by X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. Photoluminescence spectra and UV–vis spectroscopy were used to investigate the material’s UV-excited gas sensing properties and mechanism. The results showed that the composite material with molar proportion of Zn/Sn = 0.01 (SZQ 1%) was highly sensitive to NO2 at room temperature. The possible UV excitation gas sensing mechanism was discussed.