[en] Highlights: • Thermochemistry of 6-propyl-2-thiouracil – experimental and computational study. • Vapor pressure study of the 6-propyl-2-thiouracil by Knudsen effusion technique. • Enthalpies of formation of 6-propyl-2-thiouracil by rotating combustion calorimetry. • Accurate computational calculations (G3 and G4 composite methods) were performed. - Abstract: The standard (p^o = 0.1 MPa) molar enthalpy of formation of 6-propyl-2-thiouracil was derived from its standard molar energy of combustion, in oxygen, to yield CO₂ (g), N₂ (g) and H₂SO₄·115H₂O (l), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The vapor pressures as function of temperature were measured by the Knudsen effusion technique and the standard molar enthalpy of sublimation, Δ_cr^gH_m^o, at T = 298.15 K, was derived by the Clausius–Clapeyron equation. These two thermodynamic parameters yielded the standard molar enthalpy of formation, in the gaseous phase, at T = 298.15 K: −(142.5 ± 1.9) kJ mol⁻¹. This value was compared with estimates obtained from very accurate computational calculations using the G3 and G4 composite methods