Low-temperature heat capacities and high-temperature enthalpies for synthetic cu2s and cus were measured. This investigation is part of the Bureau of Mines goals to provide thermodynamic data essential to the more efficient processing of copper ores, and thereby minimize the current dislocations in energy, environment, and mineral supply. Heat capacities were measured with an adiabatic calorimeter from 5 to 310 k, and resulted in s deg 289 = 27.76 For cu2s(c) and s deg 289 = 16.05 Cal/deg mole for cus(c). Low-temperature values are tabulated for cp deg, s deg, -(g deg -h deg 0)/t, and h deg -h deg 0. Enthalpies were measured with a copper block calorimeter from 298.15 to 1,600 k for cu2s(c,1) and 289.15 to 780 k for cus(c). The thermal behavior of cus showed no transitions or other significant anomalies for the low- or high-temperature investigations. Cu2s showed reversible transitions at 376 k with an isothermal heat absorption of 0.865 Kcal/mole, 720 k with an isothermal absorption of 0.280 Kcal/mole, and approximately 1,400 k (congruent melting point) with a heat of fusion of 3.070 Kcal/mole. High-temperature data are tabulated for h deg -h deg 298, cp deg, s deg, and -(g deg - h deg 298)/t. Enthalpies are also expressed in equation form. The low- and high-temperature data were combined with data from the literature to calculate and tabulate ahf deg, agf deg, and log kf as a function of temperature.