Three dimensional (3D) porous nanostructures assembled by low-dimensional nanomaterials are widely applied in gas sensor according to porous structure which can facilitate the transport of gas molecules. In this work, fish-scale-like porous SnO₂ nanomaterials assembled from ultrathin nanosheets with thickness of 16.8 nm were synthesized by a facile hydrothermal route. Then Ag nanoparticles were decorated on the surface of SnO₂ nanosheets via one-step method to improve their gas-sensing performances. The sensing properties of pristine SnO₂ and Ag/SnO₂ nanosheets were investigated intensively. After decorating with Ag nanoparticles, the characteristics of SnO₂ based sensor for triethylamine detection were significantly improved. Especially, the Ag/SnO₂ based sensor with Ag content of 2 at% exhibited the highest triethylamine sensing sensitivity at optimum work temperature of 170 ℃. The improved sensing properties of Ag/SnO₂ sensors were attributed to the sensitizing actions of Ag nanoparticles as well as the unique hierarchical porous architecture.