The self-assembly of the dense graft copolymers ethyl cellulose-graft-polystyrene (EC-g-PS) in acetone was investigated by using dynamic light scattering (DLS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It was found that EC-g-PS copolymers can self-assemble into spherical micelles in acetone. The micelles' size increases with increasing the copolymer concentration and the PS side-chain length. Moreover, the copolymers can self-assemble into multimolecular micelles at relatively high polymer concentration while unimolecular micelles can be formed at low concentration. The micelles have a core-shell structure with the ethyl cellulose main chains in the shell and the side polystyrene chains in the core of the micelles. (C) 2008 Elsevier Ltd. All rights reserved.