Background & Objectives: 4-chlorophenolisone of the phenol derivatives that enters the environment from various sources. 4-chlrophenol ranks the primary pollutant agent. This study evaluated the efficiency and kinetics of photocatalytic degradation of 4-chlorophenol from aqueous solutions by sunlight and zinc oxide nanoparticles. Methods: This is an empirical study and Experiments were performed in the batch system. Determined dosage of ZnO nanoparticles was added to 4-chlorophenol solution (25-200ppm) and samples were allocated under the sunlight during midday hours in summer. Effects of parameters such as ZnO loading, pH, contact time and initial concentration of the polluter 4-chlrophenol were investigated. The remaining concentrations of 4-chlorophenol were analyzed using HPLC. Removal of total organic carbon was measured by TOC analyzer. Results: The results showed that removal efficiency of 4-chlorophenol was achieved 72%in presence of solar energy as means of energy source at both neutral and alkaline pH and catalyst dosage of 1.5grL-1. Efficiency increased as increasing pH and contact time. The photocatalytic degradation of 4-chlrophenol was best fitted with Langmuir–Hinshelwood model, and can be described by pseudo-first order kinetic. Conclusion: In general, 4-chlorophenols can be significantly degraded from aqueous solution by using sunlight as the energy source for the reaction and nano-sized zinc oxide as catalyst.