Novel anatase TiO2 hierarchical microspheres with selectively etched high-energy {001} crystal facets were synthesized by a facile hydrothermal method, in which etched degrees of {001} facets could be facilely tuned by pH value. Gas sensing properties of the etched TiO2 microspheres were investigated for the first time. Interestingly, it was found that the etched-TiO2 microspheres showed a much higher acetone response than that of TiO2 microspheres with intact {001} facets and slightly-etched {001} facets. The relevant gas sensing mechanism was discussed in detail. Moreover, the etched-TiO2 microspheres also showed a potential application in photocatalytic degradation of methyl orange. We expect this work would make one step closer to fully understand crystal-facets-dependent gas-sensing effect of TiO2, and provide a new TiO2 material platform for gas sensing and photcatalysis application.