Multistimuli-responsive precise morphological control over self-assembled polymers is of great importance for applications in nanoscience as drug delivery system. A novel pH, photoresponsive, and cyclodextrin-responsive block copolymer were developed to investigate the reversible morphological transition from micelles to vesicles. The azobenzene-containing block copolymer poly(ethylene oxide)-b-poly(2-(diethylamino)ethyl methacrylate-co-6-(4-phenylazo phenoxy)hexyl methacrylate) [PEO-b-P(DEAEMA-co-PPHMA)] was synthesized by atom transfer radical polymerization. This system can self-assemble into vesicles in aqueous solution at pH 8. On adjusting the solution pH to 3, there was a transition from vesicles to micelles. The same behavior, that is, transition from vesicles to micelles was also realizable on addition of beta-cyclodextrin (beta-CD) to the PEO-b-P(DEAEMA-co-PPHMA) solution at pH 8. Furthermore, after beta-CD was added, alternating irradiation of the solution with UV and visible light can also induce the reversible micelle-to-vesicle transition because of the photoinduced trans-to-cis isomerization of azobenzene units. The multistimuli-responsive precise morphological changes were studied by laser light scattering, transmission electron microscopy, and UVvis spectra. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 451457, 2012