Abstract: In this work, SnO₂/ZnO nanocomposites were successfully synthesized. By systematically characterizing their microstructure and optical properties, we conducted room-temperature NH₃ sensing tests under photo-assisted conditions across a range of concentrations, thereby elucidating the underlying ammonia-sensing mechanism of the SnO₂/ZnO composites. Different from SnO₂/ZnO nanocomposites which has reported previously , the experimentally prepared SnO₂/ZnO gas-sensing material exhibits p-type semiconductor characteristics, which provides a new potential mechanism for enhancing ZnO-based gas-sensing materials. XRD and SEM results showed that the introduction of SnO₂ helps to mitigate the agglomeration phenomenon, resulting in a reduction in the particle size of the material, while the hexagonal wurtzite structure of ZnO remains unchanged. Compared with pure ZnO, the sensor based on the SnO₂/ZnO composite material exhibited significantly enhanced ammonia sensitivity. The sensitivity to 1.39 mg/m³ and 69.5 mg/m³ NH₃ are 11% and 36%, respectively. And the sensors have beem detected 0.139 mg/m³ of NH₃ at room temperature successfully.