Thermosensitive ABC triblock copolymers with different block lengths and block orders were prepared by reversible addition fragmentation chain transfer (RAFT) polymerization. Using a nonionic macro-RAFT agent containing poly(ethylene oxide) (PEO, average degree of polymerization 17), either N-acryloylglycinamide (NAGA) or N-isopropylacrylamide (NIPAM) was first polymerized to diblock copolymers. The diblock copolymers exhibited typical thermoresponsive character of PNAGA and PNIPAM in aqueous solutions. Chain extension of the diblock copolymers was then made to prepare PEO-b-PNAGA-b-PNIPAM and PEO-b-PNIPAM-b-PNAGA triblock copolymers. Investigations of the polymer solutions showed that the triblock copolymers exhibited both UCST and LCST type transitions. The phase transitions induced the formation of polymer aggregates below UCST and above LCST, and the aggregate structures were inverted upon heating and cooling. The order of the polymer blocks with respect to PEO as well as the block sizes contributed to the thermal response.