Comparative analysis was conducted to learn the grafting of itaconic acid (LA) and glycidyl methacrylate (GMA) onto polypropylene (PP) in the course of rea active extrusion. Seven organic peroxides, which satisfactorily dissolve in PP, but do not dissolve in the monomer, were used to initiate free-radical reactions. The grafting of IA and GMA onto PP initiated by certain peroxides gave approximately equal amounts of grafted product. It was learned that the nature of peroxide initiators is decisive for grafting efficiency and degree of macromolecular degradation. To ensure a high yield of grafted product, it is advisable to use peroxides, which have thermodynamic affinity with PP and the temperature range of decomposition of which corresponds to the thermal regime of reactive extrusion. Di(tert-butyl peroxy-isopropyl)-benzene (P-14) appeared to meet for the most the, requirement, for grafting both GMA and IA. Grafting is accompanied by beta-decomposition of the chains irrespective of the type of peroxide and monomer used; hence, the MFI increases. A considerable rise in MFI was observed at a minimum peroxide concentration (0.1 wt %). Degradation of PP during modification eases its crystallization from the melt. In this case the crystallization temperature is 5 to 8.5degreesC higher than of the original PP, and the crystallinity degree increases by 20 to 60%.