A group contribution method to predict Delta H-f(298) and Delta G(f)(298) for solid inorganic salts is developed. The proposed method provides additivity constants of 23 anions, 136 cations, and 5 ligand molecules for Delta H-f(298) and 21 anions, 126 cations, and 3 ligand molecules for Delta G(f)(298). The analysis is done by data regression for Delta H-f(298) of 938 and Delta G(f)(298) of 687 solid inorganic compounds. Predictions of Delta H-f(298) and Delta G(f)(298) have a mean error of 2.57%, and 2.60%, respectively. Estimates of the relative errors for each additivity constant are also determined.