We report a poly(ethylene glycol)-poly(L-alanine)-azobenzene-poly(L-alanine)-poly(ethylene glycol) (PEG-PA-Z-PA-PEG) as a temperature and light sensitive polymer. The poly(ethylene glycol)-poly(L-alanine) diblock copolymers with a flexible-rigid block structure were coupled by an azobenzene group that undergoes a reversible configurational change between trans and cis upon exposure to UV and vis light. The single azobenzene molecule embedded in the middle of a block copolymer with a flexible (shell)-rigid (core) structure significantly affected molecular assembly, micelle size, polypeptide secondary structure, and sol-to-gel transition temperature of the polymer aqueous solution, depending on its exposure to UV or vis light. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012