The unique properties of MoS₂ nanosheets make them a promising supporting substrate for preventing the interparticle aggregation of metal–oxide–semiconductor nanomaterials. Novel composites were successfully obtained by a two-step low temperature hydrothermal method for the synthesis of SnO₂ nanoparticles dispersing on the surfaces of MoS₂ nanosheets. The morphology and structure of the as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). Owing to the supporting substrate of specific two-dimensional MoS₂ nanosheets and the superior gas-sensing performance offered by ultrasmall SnO₂ nanoparticles, the sensor based on SnO₂@MoS₂ composites exhibits high response and good selectivity to ethanol gas.