The standard enthalpies of formation of KCaH3-xFx with x = 1, 1.5, 2, 2.5 were determined by calorimetry using their reaction with hydrochloric acid aqueous solution (0.5 M HCl): Delta H-f(0) (KCaH2F, cr, 298 K) = -(874 +/- 38) kJ mol(-1) Delta H-f(0) (KCaH1.5F1.5, cr, 298 K) = -(1092 +/- 5) kJ mol(-1) Delta H-f(0) (KCaHF2, cr, 298 K) = -(1305 +/- 16) kJ mol(-1) Delta H-f(0) (KCaH0.5F2.5, cr, 298 K) = -(1524 +/- 12) kJ mol(-1) The standard enthalpy of formation of KCaH3 was estimated on the basis of the experimental measurements and on the value for potassium-calcium fluoride (KCaF3) noted in the literature: Delta H-f(0) (KCaH3, cr, 298 K) = -(442 +/- 38) kJ mol(-1) These results show that hydride compounds are less stable than fluoride homologous.