The present study involves the photocatalytic degradation of Methyl Orange (MO) and Rhodamine 6G (R6G), employing heterogeneous photocatalytic process. Photocatalytic activity of various semiconductors such as titanium dioxide (TiO2), zinc oxide (ZnO), stannic oxide (SnO2), zinc sulphide (ZnS) and cadmium sulphide (CdS) has been investigated. An attempt has been made to study the effect of process parameters viz., amount of catalyst, concentration of dye and pH on photocatalytic degradation of MO and R6G. The experiments were carried out by irradiating the aqueous solutions of dyes containing photocatalysts with UV and solar light. The rate of decolorization was estimated from residual concentration spectrophotometrically. Similar experiments were carried out by varying pH (2-10), amount of catalyst (0.25-2.0 g/l) and initial concentration of dye (5-200 mg/l). The experimental results indicated that the maximum decolorization (more than 90%) of dyes occurred with ZnO catalyst and at basic pH and the maximum adsorption of MO was noticed at pH 4 and of R6G at pH 10. The percentage reduction of MO and R6G was estimated under UV/solar system and it was found that COD reduction takes place at a faster rate under solar light as compared to UV light. In case of R6G, highest decolorizing efficiency was achieved with lower dose of catalyst (0.5 g/l) than MO (1 g/l) under similar conditions. The performance of photocatalytic system employing ZnO/solar light was observed to be better than ZnO/UV system. (c) 2006 Elsevier B.V. All rights reserved.