Decylammonium tetrachlorozincate (n-C10H21NH3)(2)ZnCl4 (C10Zn) and dodecylammonium tetrachlorozincate (n-C12H25NH3)(2)ZnCl4 (C12Zn) were synthesized and a series of their mixtures C10Zn/C12Zn were prepared. The experimental binary phase diagram of C10Zn/Cl2Zn was established by means of differential scanning calorimetry (DSC) and X-ray diffraction. In the phase diagram a stable solid compound (n-C10H21NH3)(n-C12H25NH3)ZnCl4(C10C12Zn) and two eutectoid invariants were observed. It is noticeable that the phase diagram contains solid solution ranges.