In this work, a temperature-dependent thermodynamic model based on heat capacity was proposed to predict the osmotic and mean ion activity coefficients of metal chloride aqueous solutions. The CaCl2-H2O system was used to verify the model and the results show the predicted values can well agree with the reported data, indicating that the proposed thermodynamic model is reliable. Meanwhile, the heat capacities at constant pressure of both CuCl2-H2O and NiCl2-H2O systems in the range from 298.15 to 363.15 K were calculated from the enthalpy changes determined by the calorimetric experiments. Therefore, the osmotic and mean ion activity coefficients of the two systems within 4 mol.kg(-1) were predicted in a wide temperature range with the established model. The calculated results were well consistent with the data in the literature and further indicate the thermodynamic model was reliable and convenient.