The poly(ethylene glycol)/poly(2-(N,N-dimethylamino)ethyl methacrylate) (PEG/PDMAEMA) double hydrophilic block copolymers were synthesized by atom transfer radical polymerization using mPEG-Br or Br-PEG-Br as macroinitiators. The narrow molecular weight distribution of PEG/PDMAEMA block copolymers was identified by gel permeation chromatography results. The thermosensitivity of PEG/PDMAEMA block copolymers in aqueous solution was revealed to depend significantly on pH, ionic strength, chain structure, and concentration of the block copolymers. By optimizing these factors, the cloud point temperature of PEG/PDMAEMA block copolymers can be limited within body temperature range (30-37 degrees C), which suggests that PEG/PDMAEMA block copolymers could be a good candidate for drug delivery systems. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 503-508, 2010