Poly(ethylene glycol) (PEG)-substituted cyclodextrin (CD) with an azobenzene group at the terminal of the PEG chain (6-Az-PEG600-HyCiO-beta-CD) was synthesized. The conformation of 6-Az-PEG600-HyCiO-beta-CD in aqueous solution could be controlled thermally and photochemically. At low concentration, 6-trans-Az-PEG600-HyCiO-beta-CD formed different types of self-inclusion complexes or existed in a dethreading form depending on the temperature, while at high concentration, an intermolecular complex was formed. Moreover, UV-light irradiation induced a conformational change to a self-inclusion complex where the CD cavity included the azobenzene part regardless of the concentration.