The goal of the present work is the examination of maleic anhydride (MAn) grafted impact-resistant polypropylene (T-PP), consisting of amorphous rubber and semicrystalline matrix. A special instrument to separate the rubber from the matrix is preparative temperature rising elution fractionation (TREF). Investigations of the isolated fractions permit conclusions on the course of the grafting reaction and side reactions during the modification. The present work has shown that the fractionation is just as possible in the modified products as in the raw material. It has also shown that a grafting reaction occurs mainly in the rubber phase of this two-phase polypropylene. During the grafting reaction, only small degrees of radical degradation of the homopolymeric polypropylene matrix could be detected.