Well-defined cyclic poly(N-vinylcaprolactam) (c-PNVCL) was successfully synthesized by a combination of atom transfer radical polymerization (ATRP), supramolecular self-assembly and "selective" click cyclization at a relatively high concentration (10 mg/mL). alpha-Alkyne-omega-chloro heterodifunctional PNVCL precursor (l-PNVCL-Cl) was synthesized by ATRP of N-vinylcaprolactam (NVCL), followed by its conversion to alpha-alkyne-omega-azido heterodifunctional PNVCL (I-PNVCL-N-3) via nucleophilic substitution reaction with NaN3. The intramolecular cyclization of I-PNVCL-N-3 by "selective" click reaction in aqueous micellar media afforded well-defined and narrow-disperse c-PNVCL (PDI = 1.11). The target polymer and intermediates were characterized by GPC/MALLS, H-1 NMR, and FT-IR. The thermoresponsive property of c-PNVCL and its linear precursor (l-PNVCL-N-3) was studied and compared by turbidity and dynamic light scattering (DLS) measurements, and furthermore, their self-assembly behavior was investigated by fluorescence spectroscopy and transmission electron microscopy (TEM). Cyclic poly(N-vinylcaprolactam) can self-assemble to form smaller spherical micelles in aqueous solution and possesses lower critical solution temperature (LCST) and narrower thermal phase transition range in comparison with its linear analogue. (C) 2015 Elsevier Ltd. All rights reserved.