Formaldehyde, as a harmful gas produced by materials used for decorative purposes, has a serious impact on human health, and is also the focus and difficulty of indoor environmental polution prevention; hence, designing and developing gas sensors for the selective measurement of formaldehyde at room temperature is an urgent task. Herein, a series of SnS2/SnO2 composites with hollow spherical structures were prepared by a facile hydrothermal approach for the purpose of formaldehyde sensing at room temperature. These novel hierarchical structured SnS2/SnO2 composites−based gas sensors demonstrate remarkable selectivity towards formaldehyde within the concentration range of sub-ppm (0.1 ppm) to ppm (10 ppm) at room temperature. Notably, the SnS2/SnO2−2 sensor exhibits an exceptional formaldehyde-sensing performance, featuring an ultra-high response (1.93, 0.1 ppm and 17.51, 10 ppm), as well as good repeatability, long-term stability, and an outstanding theoretical detection limit. The superior sensing capabilities of the SnS2/SnO2 composites can be attributed to multiple factors, including enhanced formaldehyde adsorption, larger specific surface area and porosity of the hollow structure, as well as the synergistic interfacial incorporation of the SnS2/SnO2 heterojunction. Overall, the excellent gas sensing performance of SnS2/SnO2 hollow spheres has opened up a new way for their detection of trace formaldehyde at room temperature.