Abstract: Thermosensitive polymers with upper critical solution temperature(UCST) are introduced,which exhibit a high critical phase transition temperature.Their phase transition and the relative factors are discussed.Various factors,such as molecule weight,hydrophobic groups of the chain,proton donor/acceptor and electrolytes in the solution,can affect the UCST of the polymers.The copolymers of UCST and LCST show a wide flexibility of thermoresponsivity,so that the application of the thermo-(responsive) polymers can be expanded.