We have synthesized the nanorods of CdS-ZnO composite by chemical method and have investigated their structure, optical and electrical properties by suitable techniques. The X-rays diffraction results prove the co-existence of CdS and ZnO in usual hexagonal structure and no peak corresponding to any intermediate phase has been identified. The above observation has been confirmed by micro-Raman study. The photo-current action spectra of CdS-ZnO nanorods show a significant enhancement of the photo-current due to visible sensitization by surface CdS layer. In an attempt to explore the catalytic activity of CdS-ZnO, the photodegradation of 3,4-dihydroxy benzoic acid has been investigated under visible irradiation from a halogen lamp. The concentration of aqueous solution of 3,4-dihydroxy benzoic acid decreases with increase in the irradiation time which is attributed to photodegradation of the benzoic acid. A possible mechanism for the redox reactions responsible for degradation of the benzoic acid has been suggested. (C) 2010 Elsevier B.V. All rights reserved.