The degradation efficiency of AC-ZnO composite photocatalyst was evaluated with solar light using an azo dye Direct blue 53 (DB53) at room temperature. Activity measurements performed under solar radiation have shown good results for the photodegradation of DB53. The synergistic effect observed was ascribed to an extended adsorption of DB53 on activated carbon followed by its transfer to ZnO where it was photocatalytically degraded. The enhanced photocatalytic activity of AC-ZnO when compared to ZnO is found to be due to this synergistic effect. A study on the effects of various parameters like concentration of dye, amount of catalyst and initial pH on the photodegradation of DB53 has been carried out to find optimum conditions. (c) 2007 Elsevier B.V. All rights reserved.