The effect of chemical non-stoichiometry and γ-irradiation on the unit cell parameters of ammonium tetrachlorozincate (NH4)2ZnCl4 (A2ZC4) has been studied. The unit cell parameters of crystal grown from solution with NH4Cl/ZnCl2 molar ratio 1:1, apparently non-stoichiometrric, are nearly the same as those given for ammonium tetrachlorozincate in the literature. The 2:1 ratio is actually ‘pseudo-stoichiometric’ due to the hygroscopic nature of ZnCl2. The unit cell parameters of crystal grown from solution with molar ratio 2:1 match those of the structure (NH4)3ZnCl5 (A3ZC5). The habit of the crystal grown in the former case, from solution with excess ZnCl2, was different from that of the crystal grown in the later case, from solution with excess (NH4)Cl. Between these two limits, a set of four samples were prepared from solutions with an excess of ZnCl2 of 20, 30, 60 and 80 wt % in order to detect exact stoichiometric composition to grow A2ZC4. Analysis by X-ray diffraction shows that the first two crystals out of this set are mixed from A2ZC4 and A3ZC5 The third and fourth crystals still contain traces of A3ZC5. Analysis of the X-ray diffraction was then confirmed by DTA study. Irradiating A2ZC4 with γ-dose of 250 kGy slightly increased the unit cell volume due to imperfections created by irradiation. Two computer programs were used to calculate the lattice constants and the results were compared