BACKGROUND: In the present study, nanocomposites of cadmium sulphide (CdS) and zinc sulphide (ZnS) on a bentonite have been prepared via an in-situ precipitation route and their catalytic behaviour was evaluated in the degradation of eosin B. RESULTS: It was found that the basal space of bentonite increased from 1.23 to 1.49 nm after CdS or ZnS nanoparticles were deposited on layers of the bentonite. The resulting CdS-bentonite and ZnS-bentonite nanocomposites can degrade eosin B from aqueous solution after 2 h under UV irradiation. CONCLUSION: A soft method for in situ synthesis of monodispersed, CdS and ZnS nanoparticles, using a reverse micelle type procedure, is reported. The synthesized CdS- and ZnS-bentonite composites combined the adsorptive ability of bentonite and the catalytic degradation ability of CdS and ZnS to remove eosin B from its aqueous solution efficiently. (C) 2009 Society of Chemical Industry