We performed the mutual anti-solvents crystallization method to make mixed crystals of organic/inorganic substances. Either aqueous ammonium chloride solution or ethanol solution of palmitic acid was sprayed on another solution at 293K, and then mixed crystals of ammonium chloride and palmitic acid crystallized out in a moment because each solvent was an antisolvent for another solution. It was found that the mass ratio of ammonium chloride in crystals were different from the mass ratio in feed two solutions. In addition the mass ratio of ammonium chloride in crystals was controlled by the concentrations of ammonium chloride and palmitic acid in two feed solutions.