In this study, CdS nanoparticles were directly grown on the surfaces of chitosan microspheres (CM) via photochemical method with irradiation from an 8W ultraviolet (UV) lamp. The nanoparticles exhibited an almost spherical shape, were closely arranged, and were immobilised on the microspheres because of the induction of the amino and hydroxyl groups of the chitosan. The CM-immobilised CdS nanoparticles showed higher activity and easier recyclability than pure CdS particles obtained in the same conditions when used in the decolourisation of methyl orange (MO) under UV-vis light. The experiments proved that the photodegradation of MO was mainly caused by the oxidisation of superoxide radicals (center dot O-2-) generated by the reaction between the electrons and the adsorbed O-2. The functional groups of CM may prevent the recombination of electron/holes and effectively promote photocatalytic reactions. This photochemical method is new, general, and promising for the immobilisation of catalyst particles on polymer microspheres, which results in enhanced activity. (C) 2014 Elsevier B.V. All rights reserved.