The morphology of multiphase polypropylene copolymers, called impact polypropylenes, was studied by Xe-129 nuclear magnetic resonance (n.m.r.) spectroscopy. The impact polypropylenes studied were composed of polypropylene homopolymer and ethylene-propylene rubber (EPR). The xenon atom is non-polar and is soluble only in the non-crystalline regions of semicrystalline polymers. Differing resonances were obtained for the differing regions in the non-crystalline phase of the impact polypropylenes. It was shown that the weight percent of EPR could be determined from the peak intensity of the resonance of the EPR regions of the polymer. Further, the average particle size of the EPR particles was shown to be determinable from the peak separation of the resonances due to the EPR particles and the non-crystalline polypropylene homopolymer. The qualitative aspects of the Xe-129 n.m.r. spectra are discussed on the basis of the microstructure and average particle size of the EPR.