Thermo-sensitivity has been introduced onto poly(ethylene terephthalate) (PET) surfaces by graft copolymer-ization of N-isopropylacrylamide (NiPAAm). The "PET surface was first photo-oxidized in the presence of H2O2, to have enriched concentration of COOH groups which were later reacted with allylamine (A1Am) to introduce vinyl end groups at the surface. These groups were used as active sites for thermally initiated graft copoly-merization of NiPAAm. The influence of solvent, monomer concentration and time on grafting has been investigated. Spectroscopic analysis confirmed the presence of (A1Am) linked to treated surfaces as well as poly (NiPAAm) grown from them. The thickness of grafted layer can be adjusted between 10 and 18 gm via grafting degree by controlling of grafting reaction parameters. Imaging in water environment revealed the reversible modification of surface morphology below and above the lower critical solution temperature (LCST) of PNiPAAm. The grafted surfaces were analyzed by colorimetric assay, ATR-FTIR, Raman, and XPS spectroscopies and Thermogravimetric analysis (TGA), and Differential scanning calorimetry (DSC).