Metal oxide-based gas sensors have drawn tremendous research interests owing to their various compositions and selective and improved performance. However, the development of a targeted metal oxide with controlled microstructures via a facile preparation procedure is still a challenge. In this work, hierarchical BiFeO₃ nano-microstructures are successfully developed through the post-modification of Bi³⁺ encapsulation with Fe-based Prussian blue microcubes followed by a sequential annealing strategy. The microstructures of the hierarchical BiFeO₃ architectures can be effectively modulated by tuning various thermolysis temperatures. Among them, the hierarchical hollow BiFeO₃ microcubes assembled from ultrathin nanosheets exhibit optimum acetone selective sensing performances with a gas response value (R_a/R_g) of 5.2 at 240 °C, rapid response/recovery times (10 s/9 s), and excellent long-term stability (for at least 30 days). The high and reproducible acetone-sensing properties are mainly attributed to the unique interior loose and porous structures with good permeability. The corresponding acetone sensing mechanism relying on the microstructure of BiFeO₃ was also discussed. This work highlights the key role of morphological evolution in the fabrication of multi-functional multimetal oxides, and thus offers new opportunities for the rational design of novel gas sensing materials.