In this study, effect of indium incorporation on the optical properties is investigated for the spray pyrolyzed onto glass substrates at 275 degrees C substrate temperature undoped and indium doped Cd0.22Zn0.78S thin films. The average optical transmittance of all the films was over 77% in the wavelength range between 450 and 800 nm. The optical band gap energies of the thin films have been investigated by the measurement of the optical absorbance as a function of wavelength. The optical absorption studies reveal that the transitions are direct band gaps of 3.02 and 3.05 eV for undoped and doped indium Cd0.22Zn0.78S thin films, respectively. The Urbach tail parameter and optical constants such as refractive index, extinction coefficient, and dielectric constants were calculated for these films. The dispersion parameters such as single-oscillator energy and dispersive energy were discussed in terms of the single-oscillator Wemple-DiDomenico model.