Carnallite (KCl.MgCl 2 .6H 2 O) is one of the most important potash minerals in nature that usually contains impurities such as water – insoluble materials, like clay and water – soluble materials such as magnesium. The aim of this study was to examine the crystallization process parameters such as temperature, brine solution density and retention time, to produce high purity carnallite and determining operational conditions by evaporating crystallization method. In this context, physical condition of solar evaporation ponds in Khor Biyabanak mine was simulated by evaporation – crystallization process in a static state with temperatures of 15, 25, 35 and 45 °C. During this process, by increasing the density of the solution from 1.200 to 1.450 g/cm 3 (in according evaporative ponds of Khor Biyabanak mine), the quantity and quality of various precipitated salts were examined. The results showed that halite was produced during the crystallization process, halite was produced and a large percentage of halite in the final density of the solution was transfer to the crystal phase. The initial density of brine was saturated with sodium and the final density of brine was saturated with magnesium and calcium. The best conditions for crystallization of carnallite show was the density range from 1.360 to 1.450 g/cm 3 at 45?C temperature, in which calcium impurities were negligible and the grades of halite, carnallite considered were 44% and 56%, respectively.