Porous SnO₂ hierarchical architectures were synthesized by calcining the precipitates prepared through a facile one-step hydrothermal synthesis method. Field emission scanning electron microscopic and transmission electron microscopic results revealed that these hierarchical nanostructures were built from two-dimensional porous nanosheets. The morphology of the prepared products could be tailored by changing the precursor concentration and reaction time. On the basis of experimental results, a possible mechanism for the formation of the three-dimensional SnO₂ hierarchical nanostructure was speculated. Moreover, gas sensing tests showed that the sensor using porous SnO₂ hierarchical nanosheets after annealing at 600 °C for 2 h exhibited better gas sensing properties compared with the sensor based on conventionally prepared SnO₂ nanoparticles. The enhancement in gas sensing properties was attributed to their unique structures.