Crystallizations of KCl from water and reagent grade potassium chloride solution with and without magnesium sulfate and magnesium chloride as impurities were conducted in a one liter continuous MSMPR cooling crystallizer. A series of experiments at a constant operating temperature, various feed temperatures and magnesium and sulfate ions concentrations were carried out to investigate the effect of the type and concentration of impurities on the width of the meta-stable zone, crystal size distribution, crystal habit, crystal purity, growth rate, nucleation rate, and aggregation index. The width of the meta-stable zone increased with impurity concentrations of both magnesium and sulfate ions alike. Sulfate ion increased the mean crystal size at all concentrations, whereas the initial increase in mean crystal size at low magnesium concentrations was moderated at higher concentrations. Polycrystals formation was significant with and without impurities. The crystal surface became irregular at higher sulfate ion concentrations. The impurity incorporation within KCl crystals decreased with crystal size and was much higher in the case of magnesium sulfate. Secondary nucleation rate was unaffected and growth rate was altered in the presence of both impurities, and the influence was apparently independent of the effect upon the meta-stable zone width. The effect of impurities was suppressed with increase in suspension density.