We have developed new methods to prepare various well-defined stimuli-responsive polymers via living/controlled cationic polymerization, because the stimuli-responsive polymers have attracted significant interest in various fields. This presentation focuses on the following topics: (i) development of living cationic polymerization, (ii) highly stereospecific living cationic polymerization of N-vinylcarbazole, (iii) alternating cationic copolymerization and sequence-controlled polymers with precisely placed breakable bonds, (iv) precise synthesis of various stimuli-responsive block or star-shaped copolymers: block copolymers with UCST-type segment and LCST-type segment exhibiting shape-switching self-assembly in water, quantitative and ultrafast synthesis of well-defined star-shaped polystyrenes, synthesis of block or graft copolymers containing polylactides.