The effect of laser illumination on aqueous solutions ofstar-like Dextran-graft-Polyacrylamide copolymer with incorporated gold nanoparticles was studied by holographic interferometry technique. The method is based on observing in real time the value of the change of the refractive index of this solution during and after its illumination with laser light from the absorption range of Au nanoparticles. An unusual effect of the localization of the radiation heating of the solution volume in the region of the laser beam passage was observed. Thermal diffusion into the non-illuminated volume is practically absent. It is concluded that the relaxation of the energy of radiation excitation of Au nanoparticles occurs mainly within the large Dextran-graft-Polyacrylamide macromolecules.