ZnSO4 center dot 7H(2)O is a promising thermochemical heat storage material. In this paper, we report a detailed thermodynamic study of ZnSO4 center dot 7H(2)O based on hydration/dehydration, cyclicability, and water sorption performance. The TG-DSC measurements reported that at below 120 degrees C, 1747 and 1298 J g(-1)enthalpy was recorded for dehydration and hydration, respectively. The relative-humidity study showed that at 75% RH (0.148 g/g), the water sorption can be significantly improved compared to lower humidity (65% 0.131). The XRD study highlighted that the main structure of ZnSO4 after thermal treatment remains unchanged.