Photo-responsive microgels were prepared by taking advantage of the interaction between Tween 20-coumarin conjugate (TCC) and polymeric β-cyclodextrin (PβCD). TCC was prepared by covalently attaching coumarin to the hydroxyl group of the head (PEO segment) of Tween 20. The molar ratio of coumarin residue and Tween 20 was 1 : 1, determined on the 1H NMR spectrum. PβCD was prepared by reacting epichlorohydrins (EPI) with the hydroxyl groups of βCDs. The primary hydroxyl groups participated in the polymerization reaction, evidenced by the 13C NMR spectrum. The CD content in PβCD, determined by a colorimetric method, was 37.4%. Microgels were prepared by adding TCC to the aqueous solution PβCD (20%, w/v) so the molar ratio of TCC to βCD residue was 0.72 : 1. The shape was spherical on SEM photo and optical microscopic photo, and the diameter, measured on light scattering equipment, was a few micrometers. The size dramatically decreased by the irradiation of λ at 365 nm, possibly due to the photo-dimerization of coumarin residue of TCC. Thr size of the photo-treated microgel markedly increased by the irradiation of λ at 254 nm, possibly due to the de-dimerization of the coumarin residue dimers.