We reported the synthesis of double thermo-responsive block copolymers comprised of a poly(N-isopropylacrylamide (NIPAAm)) block and a poly(NIPAAm-co-N-(hydroxymethyl)acrylamide (HMAAm)) block, which was synthesized using an atom transfer radical polymerization (ATRP) technique. The cloud point of the poly(NIPAAm-co-HMAAm) (NH) block could be easily controlled by altering the HMAAm content. Below the cloud point of polyNIPAAm (N) block, the block copolymers were completely dissolved. Between the cloud points of each block, the block copolymer formed the aggregate structure that Could be constructed with the hydrated NH shell and the dehydrated N core. Moreover with increases in temperature, the diameter decreased due to the dehydration of the NH block shell. The response was completely reversible by changes in temperature, as confirmed by H-1 NMR, turbidity, and FE-SEM measurements. (C) 2009 Elsevier Inc. All rights reserved.