US nanoparticles were homogeneously coated on multimalled carbon nanotubes by an in situ method through introducing thiol groups onto the tube wall using a novel method. A cationic polyelectrolyte containing reactive imine groups, polyethyleneimine (PEI), was firstly adsorbed on the surface of nanotubes. 3-Mercaptopropionic acid (MPA) was then anchored by an amidation reaction between its carboxyl group and the imine group of the polyelectrolyte under the activation of carbodiimide reagents. These-SH terminated MWCNTs were coated with US nanoparticles by an in situ method. The phase composition, microstructure, and the UV-vis properties of the US coated MWCNTs were characterized. The addition of the carbodiimide reagents played an important role in linking the MPA with PEI covalently and subsequently coating the MWCNTs with US homogeneously. A blue shift in the absorption edge was observed for the MWCNTs-CdS hybrid material due to the quantum size effect. (c) 2004 Elsevier B.V. All rights reserved.