A combination of static and dynamic laser light scattering has revealed that at temperatures highe than ,33 ±C a linear poly( N-isopropylacrylamide) chain grafted with poly(ethylene oxide) (PNIPAMg-PEO) in water can undergo a “coil-to-globule” transition to form a stable single chain core-shell nanostructure with the collapsed PNIPAM chain backbone as the hydrophobic core and the grafte PEO branches as the hydrophilic shell. It was also found that there still exists ,75% of water in the collapsed hydrophobic core which might be useful for biomedical applications because the core-shell nanostructure can be easily switched on and off by a simple temperature variation of 1 2±C. [S0031-9007(97)05032-1]