Mixed crystals of potassium-ammonium zinc chloride in different concentrations were grown from aqueous solution employing the techniques of slow cooling and controlled evaporation. Powder x-ray diffraction studies were carried out on the grown crystals. The comparison between lattice parameters a, b and c are experimentally determined and calculated by Vegad's law. The concentration of K+ ions in the crystals was measured by the atomic absorption technique. The crystal morphology changed considerably by increasing K+ concentration. The optical absorption coefficient (α) indicated strong influence changing concentration. The optical energy gap was found to decrease with increasing K+ concentration.