The specific (c(p)) and molar (C-p) heat capacities of the mixtures of hexamethylphosphoramide (HMPA, or h) with water (w) have been measured using an adiabatic calorimetry at T= (283.15, 288.15, 293.15, and 298.15) K and ambient pressure. Based on the results obtained, the excess molar heat capacities of the mixtures, C-p(E), as well as apparent molar heat capacities of each component, C-p,C-phi,C-i (down to its infinite dilution, C-p,i(o)), have been calculated. The C-p(E) values are positive up to HMPA mole fractions being x(h) approximate to 0.9 and the dC(p)(E)/dT derivative undergoes a positive-to-negative sign inversion at x(h) = 0.33. Both concentration and temperature dependences of C-p,phi,(i) have also a complex character. The correlations of molar heat capacity properties with volume-related those for (H2O + HMPA) at the same temperatures have been discussed, too.
