In order to obtain the water-soluble, temperature sensitive polymer and activated copolymer, the radiation polymerizaton of N-isopropylacrylamide(NIPAAm), radiation copolymerization of NIPAAm and N-acryloxysuccide (NASI)in aqueous solution or in buffer solution (PBS pH=7.4) have been carried out by γ-rays from ,60,Co source at room temperature. The optimum dose range (1—7 kGy), dose rate (,>,40 Gy/min) and monomer concentration (1%) were chosen through determing the monomer conversion yield and molecular weight (M,w,=6.8×10,5,) of product. Synthesis of the reversible linear polymer was performed in tetrahydrofuran(THF) as well. In this way a white powder product could be obtained which possesses of thermally reversible property too, when it was dissolved in water or PBS. The only disadvantags of this method is that the molecular weight of the polymer produced in THF was much lower than that in aqueous solution.