Fourier transform infrared (FTIR) in combination with UV/Vis spectrophotometric analysis were performed to study the role of UV irradiation on the commercial samples of pristine high-density polyethylene (HDPE) films. X-ray diffraction data reveals an increase in the percent crystallinity which correlated and fitted linearly with irradiation times. FTIR experimental absorption spectra for commercial (HDPE) sample and other samples that irradiated with UV lamp for different prolonged time intervals shows the maintenance of main pseudo four characteristic bands in their positions with different intensities. Careful analysis of FT-IR bands reveals a clear variation in both band position and intensity for samples that irradiated up to 16 hours. UV/Vis. electronic spectra reveal the presence of charge transfer band in the UV region around 210 nm with a small change in their fundamental absorption edge and optical energy gap without any evidence for any other band till the end of measurements. Absorbance intensity was found to varies in relation to the irradiation time and sample thickness. Obtained data may be interpreted in terms of free radical and oxidation reactions of polyethylene.