Fluorine-containing amphiphilic ABA triblock copolymers, poly(2-hydroxyethyl vinyl ether)-block-poly[2-(2,2,3,3,3-pentafluoropropoxy)ethyl vinyl ether]-block-poly(2-hydroxyethyl vinyl ether) [poly(HOVE-b-PFPOVE-b-HOVE)] (HFH), poly[2(2,2,3,3,3-pentafluoropropoxy)ethyl vinyl ether] -block-poly(2-hydroxyethyl vinyl ether)block -poly[2-(2,2,3,3,3-pentafluoropropoxy)ethyl vinyl ether] [poly(PFPOVE-b-HOVEb-PFPOVE)] (FHF), and poly(n-butyl vinyl ether)-block-poly(2-hydroxyethyl vinyl ether)-block-poly(n-butyl vinyl ether) [poly(NBVE-b-HOVE-b-NBVE)] (LHL), were synthesized, and their behavior in water was investigated. The aforementioned polymers were prepared by sequential living cationic polymerization of 2-acetoxyethyl vinyl ether (AcOVE) and PFPOVE or NBVE, followed by hydrolysis of acetyl groups in polyAcOVE. FHF and LHL formed a hydrogel in water, whereas HFH gave a homogeneous aqueous solution. In addition, the gel-forming concentration of FHF was much lower than that of corresponding LHL. Surface-tension measurements of the aqueous polymer solutions revealed that all the triblock copolymers synthesized formed micelles or aggregates above about 1.0 x 10(-4) mol/L. The surface tensions of HFH and FHF solutions above the critical micelle concentration were lower than those of LHL, indicating high surface activity of fluorine-containing triblock copolymers. Small-angle X-ray scattering measurements revealed that HFH formed a core-shell sperical micelle in 1 wt % aqueous solutions, whereas the other block copolymers caused more complicated assembly in the solutions.