Leaf-like SnO₂ hierarchical architectures were successfully synthesized via a facile template-free hydrothermal synthesis method. The observations with field emission scanning electron microscopic and transmission electron microscopy demonstrated that the uniform and independent leaf-like SnO₂ architectures were obtained, and each dendrite was consisted by a main stem with two groups of highly symmetric and parallel branch. To investigate the effect of diammonium phosphate and the formation process of hierarchical SnO₂ leaf-like microstructure, the controlled experiments of the hydrothermal process with different amounts of diammonium phosphate and different reaction times have been carried out systematically. Based on the experimental results, a possible formation mechanism of SnO₂ hierarchical architecture was speculated. In addition, the gas sensing performances of the as-prepared products were investigated and the results revealed that the sensor based on the unique leaf-like SnO₂ hierarchical architectures exhibited high response and good selectivity properties to NO₂ at low working temperature.