Hyperbranched poly(3-ethyl-3-oxetanemetha-nol)-graft-poly(2-dimethylaminoethyl methacrylate) (HP-g-DMA) with a three-demensional structure was synthesized via oxyanionic polymerization. The hydroxyl groups of hyper-branched poly(3-ethyi-3-oxetanemethanol) (HP) reacted with KH and conversed into potassium alcoholate macroinitiators with high initiating efficiencies. High monomer conversion (>95%) was obtained and no residual macroinitiators or monomer was observed. UV-visible spectra indicate that the aqueous solution of the HP-g-DMA exhibited the lowermost critical solution temperature (LCST). The LCST was influ-enced by the chain length of DMA and pH condition of solu-tion. It is found that LCST decreased with increasing DMA chain length or increasing pH value of solution. Hyper-branched poly (3-ethyl-3-oxetanemetha-nol) -graft-poly (2-dimethylaminoethyl methacrylate) (HP-g- DMA) with a three-demensional structure was synthesized via oxyanionic polymerization. The hydroxyl groups of hyper- (3-ethyi-3-oxetanemethanol) (HP) reacted with KH and conversed into potassium alcoholate macroinitiators with high initiating efficiencies.> 95%) was obtained and no residual macroinitiators or monomer was observed. that the aqueous solution of the HP-g-DMA showed the lowermost critical solution temperature (LCST). The LCST was influ- enced by the chain length of DMA and pH condition of solu- tion. It is found that LCST decreased with increasing DMA chain length or increasing pH value of solution.