The enthalpies of interaction of XeF5[BF4](cr) (XeF6 · BF3) with water and an aqueous solution of alkali were measured on an isothermic-shell calorimeter at 298.15 K. The results of measurements and literature data were used to calculate the standard enthalpy of formation of XeF5[BF4](cr) at 298.15 K, ΔfH∘ = −1547 ± 10 kJ/mol.