SnO₂ microspheres in a composite with Pt nanoparticles (0, 0.5, 1.5, 2.5, 5.0 mol% Pt loading) were synthesized by a solvothermal method. The crystal structure, morphology, and specific surface area were thoroughly characterized. It is found that the Pt–SnO₂ nanocomposites consist of a large amount of small spheres with average diameters up to hundreds of nanometers, and every small sphere is composed of numerous primary nanocrystallites with an average size of about 8 nm. Compared with the pristine SnO₂, the presence of Pt nanoparticles has no influence on the growth behavior of the SnO₂ microspheres. The gas sensors based SnO₂ microspheres in a composite with Pt nanoparticles not only show a lower operating temperature and immensely enhanced responses, but also exhibit a faster response and recovery speeds and remarkable stability to methanol, especially the 5.0 mol% Pt–SnO₂ nanocomposite. The gas sensor based on the 5.0 mol% Pt–SnO₂ nanocomposite exhibits a response value of 190.88 to 100 ppm methanol at a low operating temperature of 80 °C, while the gas sensor based on pristine SnO₂ only displayed a response value of 19.38 at an operating temperature of 200 °C. The reasonable explanation of the gas-sensing performance enhancement for the gas sensors based on Pt–SnO₂ nanocomposites is attributed to the strong spillover effect of the Pt nanoparticles and the electronic interaction between Pt nanoparticles and SnO₂ microspheres, both of which promoted the low temperature gas-sensing performance.