Asymmetric hollow particles were fabricated from the self-assembly of block copolymers poly(N-isopropylacrylamide)-block-poly(4-vinylpyridine) (PNIPAM-b-P4VP) and poly(ethylene glycol)-block-poly(acrylic acid) (PEG-b-PAA) in water. The shell of the asymmetric hollow particle was a polyion complex layer which acted as a semipermeable membrane. outside the shell were PEG hydrophilic layers and inside were thermo-sensitive PNIPAM chains. When temperature was higher than the lower critical solution temperature (LCST) of PNIPAM, it became insoluble and collapsed onto the shrinking shell to form a hydrophobic lumen. The whole process was characterized by dynamic light scattering (DLS), static light scattering (SLS), transmission electron microscopy (TEM), atom force microscopy (AFM) and nuclear magnetic resonance (NMR). (C) 2008 Elsevier Ltd. All rights reserved.