Heat capacity of K 2 ZnBr 4 was measured by adiabatic calorimetry between 13 and 300 K. The αII-αI phase transition was observed as a typical second-order type of anomaly at 156 K. The enthalpy and entropy of transition were: determined as 499.7 J mol - 1 and 3.91 J K - 1 mol - 1 , respectively. The data were compared with those of the as-grown crystals of K 2 ZnBr 4 from the aqueous solution, and the effects of water included in the crystals are discussed.