Graft copolymerization of acrylonitrile (AN) and its binary mixture with 4-vinyl pyridine (4-VP) onto isotactic polypropylene powder in aqueous medium, using gamma-rays as an initiator, was studied. Optimum conditions for affording maximum percentage of grafting were evaluated. Rate of grafting (Rg) of AN and binary mixture (4-VP + AN) was determined as a function of total initial monomer concentrations. The graft copolymers were characterized by IR spectroscopy and thermogravimetric analysis.