This research work is devoted to studying optical properties of zinc selenide (ZnSe) thin films deposited by electron beam evaporation technique and annealed at different temperatures in a nitrogen environment. The structural analysis by X-ray diffraction confirmed that the obtained ZnSe films had cubic zinc-blende structure with preferred orientation along plane (111). Based on Swanepoel's envelope method, some important optical parameters such as absorption coefficient, extinction coefficient, refractive index and optical band gap, were evaluated through the transmission spectrum ranging from 300 to 1500 nm at room temperature. The optical band gap increased from 2.52 to 2.65 eV with the increasing annealing temperature. However, both the thickness and refractive index of the films decreased. In addition, the dispersion parameters of the refractive index and energy were also studied by using Wemple-DiDomenico single oscillator model.