A novel photo-sensitive telechelic poly(N,N-dimethylaminoethyl methacrylate) with coumarin end (C-PDMAEMA) was prepared with DAMEMA as monomer, coumarin-containing disulfide (C-S-S-C) as a chain transfer agent in the presence of Bu₃P and water, AIBN as initiator. The polymer was characterized with ¹H NMR, GPC and FTIR spectroscopes. It was found that the polymer can immediately form polymer nano-aggregate in aqueous solution. And the coumarin end group of the polymer can be reversibly photo-dimerized upon 365 and 254 nm irradiation. The hydrodynamic size analysis determined by Malvern Zetasizer Nano-ZS instrument and the TEM observations showed that the average size of the polymer nano-aggregate increased upon 365 nm irradition and decreased upon the subsequent 254 nm light.