Chitosan capped CdS (CS/CdS) composite nanoparticles were prepared by biomimetic synthesis method under mild condition. The CS/CdS composite catalyst was characterized by XRD, SEM, TEM and TGA, which indicated the successful formation of nanosized hexagonal phase of US on chitosan. Visible light photocatalytic decolourization of C. I. Acid Red 66 (AR 66) was carried out by employing this innovative composite catalyst. The effects of catalyst amount, initial dye concentration and initial pH of solution on decolourization were investigated. The kinetics of photocatalytic decolourization was found to follow a pseudo-first-order according to Langmiur-Hinshelwood (L-H) model. UV-vis spectra were analyzed to prove that AR 66 dye can be decolourized effectively by chitosan capped US composite nanoparticles under visible light irradiation. In addition, the recycle and reuse of the catalyst were examined, and the results showed that dye decolourization efficiency was still about 80.1 % after 60 min of reaction time when the catalyst was used for 5 times. (C) 2009 Elsevier B.V. All rights reserved.