Abstract: A series of poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) with a degree of polymerization up to 300 was successfully synthesized by atom transfer radical polymerization (ATRP) in aqueous medium at 30 ℃ using CuBr-CuBr2 as catalyst and pentamethyl diethylenetriamine(PMDETA) as ligand. Results of 1H-NMR showed that the polymerization process was in accordance with the first order kinetic characteristics. The thermosensitivity of the resulting PDMAEMA was determined by turbidity measurements using UV-Vis spectroscopy. Results showed that, when the chain length of PDMAEMA increased, the lower critical solution temperature (LCST) could decrease to 31.4 ℃.