The combustion energy of thioproline was determined by the precision rotating-bomb calorimeter at 298.15 K to be ΔcU= –2469.301.44 kJ mol–1. From the results and other auxiliary quantities, the standard molar enthalpy of combustion and the standard molar enthalpy of formation of thioproline were calculated to be ΔcHmθC4H7NO2S, (s), 298.15 K= –2469.921.44 kJ mol–1 and ΔfHmθC4H7NO2S, (s), 298.15K= –401.331.54 kJ mol–1.