Double hydrophilic copolymers (PEG-b-PCDs) with one PEG block and another block containing beta-cyclodextrin (beta-CD) units were synthesized by macromolecular substitution reaction. Via a dialysis procedure, complex assemblies with a core shell structure were prepared using PEG-b-PCDs in the presence of a hydrophobic homopolymer poly(beta-benzyl L-aspartate) (PBLA). The hydrophobic PBLA resided preferably in the cores of assemblies, while the extending PEG chains acted as the outer shell. Host-guest interaction between (beta-CD and hydrophobic benzyl group was found to mediate the formation of the assemblies, where PEG-b-PCD and PBLA served as the host and guest macromolecules, respectively. The particle size of the assemblies could be modulated by the composition of the host PEG-b-PCD copolymer. The molecular weight of the guest polymer also had a significant effect on the size of the assemblies. The assemblies prepared from the host and guest polymer pair were stable during a long-term storage. These assemblies could also be successfully reconstituted after freeze-drying. The assemblies may therefore be used as novel nanocarriers for the delivery of hydrophobic drugs. (C) 2011 Elsevier Ltd. All rights reserved.