In this work, a thin film of Modification Waste Polystyrene (MPS) with Sulfuric acid have been prepared by using spin coating method. The optical properties have been evaluated by means of transmittance and reflectance spectra, measured in the wavelength range of 300 to 900 nm. The thin films' optical constants, including refractive index (n) and extinction coefficient (k), were calculated. The studies on optical absorption spectra studies revealed that the indirect allowed transition is the absorption mechanism. The optical energy gap has been calculated to be 2.554 eV.