Efficient photocatalytic degradation of a commercial low-density polyethylene (LDPE) was developed via incorporation of polystyrene grafted ZnO nanoparticles. The free radical reaction was used for grafting process of the styrene monomer on the ZnO nanoparticle. Neat LDPE and composite LDPE films, containing pristine and grafted ZnO nanoparticles, were prepared via film blowing techniques. Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were employed for investigation of successful grafting process and amount of grafting determinations. Tensile tests and weight loss assessments were used for evaluation of the photocatalytic degradation. The FTIR and TGA results confirmed the successful grafting, whereas the TGA results determined 16 and 39 wt% of polystyrene grafting on the ZnO nanoparticles. The mechanical tests showed that both incorporation of the nanoparticles and grafting increased the tensile strength of the prepared LDPE films. Photocatalytic degradation evaluations revealed that incorporation of ZnO nanoparticles improved the degradation in the composites films after 200-h UV irradiation. The polystyrene grafting increased the ZnO nanoparticle's dispersion, whereas the increase in grafting from 15 to 39 wt% mitigated the efficiency of the ZnO photocatalytic performance. It was possibly due to the surrounding polystyrene that reduced the nanoparticle UV absorption.