The oxidation process of samariumoxysulfide was studied in the temperature range of 500-1000 °C. Our DTA investigation allowed for establishing the main thermodynamic (∆Hº exp = -654.6 kJ/mol) and kinetic characteristics of the process (E a = 244 kJ/mol, A = 2 × 10 10). The enthalpy value of samarium oxysulfate (ΔHºf (Sm 2O 2SO 4(monocl)) = -2294.0 kJ/mol) formation was calculated. The calculated process enthalpy value coincides with the value determined in the experiment. It was established that samarium oxysulfate crystallizes in the monoclinic symmetry class and its crystal structure belongs to space group C2/ c with unit cell parameters a = 13.7442 (2), b = 4.20178 (4) and c = 8.16711 (8)Å, β = 107.224 (1)°, V = 450.498 (9)Å 3, Z = 4. The main elements of the crystalline structure are obtained and the cation coordination environment is analyzed in detail. Vibrational spectroscopy methods confirmed the structural model adequacy. The Sm 2O 2SO 4luminescence spectra exhibit three main bands easily assignable to the transitions from 4G 5/2 state to 6H 5/2, 6H 7/2, and 6H 9/2 multiplets.