Y2O3 dumbbells, microspheres, and nanosheets were synthesized by a facile hydrothermal procedure followed by calcination. Electron microscopy, X-ray diffraction, and N2 adsorption measurements were used to characterize the yttrium oxide microstructures. On the basis of a time-dependent study of nanostructure evolution and the effect of other processing parameters, a kinetic “homogeneous nucleation–self assembly–anisotropic growth” mechanism is proposed to explain the growth of these microstructures under hydrothermal conditions. The sensitivity of as-prepared Y2O3 structures to a series of gaseous chemicals was examined by using a homemade cataluminescence sensing system. The designed cataluminescence sensor based on the yttrium oxide dumbbells shows good sensing performance for 16 common volatile organic compounds.