Optical transmittance measurements were carried out near the absorption edge of (NH4)2ZnCl4:xSr2+ single crystals, where x = 0.00, 0.020, 0.039, 0.087 or 0.144 wt%. The dependence of the absorption coefficient (α) on photon energy in the range 3.4-6.4 eV and on temperature in the range 276-350 K was examined. With increasing temperature the absorption edge was shifted to the lower energy side; this shift was attributed to the temperature dependence of electron-lattice interactions. Due to the presence of Sr2+ in (NH4)2ZnCl4:xSr2+ a change in the absorption band centred at 5.30 eV was observed. In the case of higher strontium doping, the optical absorption coefficient showed a pre-transition stage just before the onset of the band-to-band transition. Exponential dependence of α on h according to the Urbach rule was observed and the Urbach parameters were determined. The steepness parameter was strongly affected by doping; its behaviour at 319 K evidently showed the antiferroelectric to commensurate phase transition. The temperature dependence of Eg was also estimated using data for the steepness parameter, and hence Eg at different temperatures and Sr2+ concentrations was evaluated