In the present paper,the preparation and properties of Eu(Ⅲ) on poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AAc)) were described.At first,P(NIPAM-co-AAc) microgel nanoparticles were prepared by the precipitation copolymerization of N-isopropylacrylamide with acrylic acid in the presence of N,N-methylenebisacrylamide in water.The morphology and size of the P(NIPAM-co-AAc) nanoparticles were characterized by the scanning electron microscope (SEM) method.The result of SEM shows that the sample is uniformly sized spherical particle and the average particle size of the P(NIPAM-co-AAc) is about 365 nm.Then,EuCl 3 was chosen to interact with P(NIPAM-co-AAc) nanoparticles and formed the complex of P(NIPAM-co-AAc)-Eu(Ⅲ).The complex was characterized by Fourier transform infrared spectroscopy,ultraviolet-visible and fluorescence spectroscopy.It was found that the complex shows thermo-responsive fluorescence from the experimental results.There exists a energy transfer between the polymer ligand and the Eu(Ⅲ),which can enhance fluorescence emission of the polymer ligand and Eu(Ⅲ) at the same time.The LCST of P(NIPAM-co-AAc) containing Eu(Ⅲ) has changed little after the formation of the complex of P(NIPAM-co-AAc)-Eu(Ⅲ).Therefore,the complex can be used for developing the new applications in biomedical and fluorescence field.