The ZnS_xSe_1-x thin films were deposited by the quasi-closed volume technique under vacuum. The film structure was studied by X-ray diffraction technique. The studies shown the films are polycrystalline and have a zinc blende structure. The spectral dependences of transmission, reflection, absorption and refraction index were studied. Values of band gap energy determined from the reflectance and absorption spectra are in good agreement with the theoretical values E_g.