Preparation of temperature-sensitive core-shell composite polymer particles was carried out by seeded emulsion copolymerization of dimethylaminoethyl methacrylate and ethylene glycol dimethacrylate with submicron-sized polystyrene seed particles as core. The lower critical solution temperature (LCST) of the core-shell composite was about 35°C, while the LCST could be controlled toward higher or lower temperatures by copolymerizing the shell layer with hydrophilic/hydrophobic vinyl comonomer.