The isochoric heat capacity and the PVT of 50 mol% mixtures of n-pentane + n-heptane in the temperature range 300-500 K have been measured in the two-phase state and the liquid phase including phase equilibria. The measurements were made on samples of constant mass contained in a high-temperature calorimeter-piesometer vessel of constant volume. The phase equilibrium line was obtained from the break in the function C-v =f(T) along the isochores.