The standard molar enthalpy of formation of Y2Ba4Cu7O14.916 at T = 298.15K has been determined by solution calorimetry to be : Delta(f)H(m)(0) (Y2Ba4Cu7O14.916, cr, 298.15 K) = (-5465.7 +/- 7)kJ.mol(-1). During the experiment the molar enthalpies of reaction of the Y2Ba4Cu7O14.916 high-temperature superconductor and metallic yttrium with 1.07N HCl have been measured in a hermetic rotating calorimeter equipped with an isothermal jacket.