Detailed scintillation properties of Sc2O3, especially gamma-ray response, are not well studied because of low density and low effective atomic number of this compound. They are reported in this paper. Sc2O3 single crystals grown by the micro-pulling-down method and Sc2O3 translucent ceramics produced by the spark plasma sintering are analyzed. Optical, luminescence, and scintillation properties of these single- and poly-crystalline solids are discussed and compared based on examination of their optical transmittance, radio-luminescence spectra, light yields under gamma-ray excitation, non-proportionality, energy resolution, and scintillation decay profiles. Spectrally corrected light yields of the Sc2O3 single crystals and Sc2O3 ceramics were approximately 7,700 and 19,200 photons/MeV, respectively.