Based on the previous research, it has been revealed that zinc oxide nanoparticles in presence of polyethylene glycol (ZnO-PEG) have high potential for photocatalytic degradation of industrial dye wastewater. However, the study on the performance of ZnO-PEG and ZnO−CC nanoparticles to treat palm oil mill secondary effluent (POMSE) is still limited. In addition, the optimum condition for photocatalytic degradation of POMSE in presence of ZnO-PEG and ZnO−CC nanoparticles under two different power of light source which are 18 W and 500 W also not been well discovered. The aim of this study was to observe the photocatalytic degradation efficiency through percentage of color reduction for POMSE after being treated. Based on this study, the best photocatalyst and the optimum condition for photocatalytic degradation of POMSE had been identified under 18 W of UV irradiation in the presence of 0.5 g/L of ZnO-PEG nanoparticles. While for the optimum condition, it had been found that the reduction percentage of color removal (70.75 %), turbidity (87.33 %), COD (68.31 %), BOD (650.1 mg/L) were obtained. Thus, it is believed that this research will attract much attention from researchers globally, as the benefits of an environmental approach has always been in the forefront of sustainable development.