Branched copolymers Dextran-graft-Polyacrylamide (D-g-PAA) with star-like architecture of macromolecules and linear Polyacrylamide (PAA) were used for in situ synthesis of Ag nanoparticles. Aqueous silver colloids were characterized by UV-vis spectroscopy, TEM and dynamic light scattering. The internal structure of polymer matrices in solution affects the Ag nanoparticle formation and stability of colloid systems. Branched structure of D-g-PAA macromolecules provides obtaining of stable silver colloids even at high temperature when linear PAA matrix is not efficient.