Modi®cation of dextrin by tert-butylperoxy methanol or its acylation with cyclic anhydride containing a peroxide group resulted in macro-initiators with randomly located peroxide fragments in the polysaccharide.When dextran was oxidized with iodic acid, dialdehydedextran was obtained. Its aldehyde groups reacted with tert-butyl hydroperoxide to give functional peroxide groups. The content of peroxide fragments depended directly on the ratio of reagents.The resulting macro-initiators may be used for synthesizing graft copolymers with polystyrene on poly(butyl acrylate) containing polysaccharide.