The influence of dibutyl phthalate, dioctyl phthalate, dimethyl terephthalate, diethyl terephthalate, and dioctyl terephthalate-plasticizers on poly (para-methoxy styrene) photodegradation was investigated by UV-vis, fluorescence, and FT-IR spectroscopic methods. The increase in irradiation time caused an increase in the absorption band of the polymer and an increase in the absorption of new band at longer wavelength, thus indicating a possibility of photodegradation of polymer films. The study on poly (para-methoxy styrene) photodegradation was also compared to varying phthalate and terephthalate plasticizers in order to provide an understanding of its photodegradation vis the presence of phthalates and terephthalates plasticizers. The decrease in the excimer fluorescence upon the increase in the time of exposure to UV-radiation provides an evidence for the degradation of polymeric chains through a chin scission processes. The increase in the photodegradation of the polymer increased with the increase in the bulkiness of added plasticizer molecule. IR-spectra of irradiated pure and blended polymer films indicated that the photodegradation of the polymer occurred, by the formation of new absorption bands, and the increase in the intensity of other bands.