Cobalt ion (Co) doped ZnO (CDZ), prepared by simple soft chemical method and calcined at 300 degrees C, was characterized by XRD, FE-SEM, TEM, FT-IR, DRS and EPR. The EPR and DRS suggest that Co2+ is in a tetrahedral coordination in the ZnO matrix. The size of the nanoparticle is 5-30 nm by TEM. Different experimental parameters were standardized to achieve complete degradation of phenol under visible light. The following parameters such as effects of pH, phenol concentrations, mass of catalyst, and kinetics of degradation have been studied. The degradation of phenol has been monitored by UV-Visible spectrum and COD analysis. The visible photo degradation of phenol was found to exhibit pseudo-first order kinetics. Degradation intermediates were identified by ESI-Mass and HPLC analysis. Under visible light, the doped oxide effectively catalyzes the oxidation of phenol in water. (C) 2013 Elsevier B.V. All rights reserved.