Reactive blending of polypropylene (PP) and amorphous polyamide (aPA) was carried out using a gram-scale mixer. Maleic anhydride-grafted PP was used as a reactive PP. Time resolved light scattering analysis showed that, compared with non reactive systems, the reactive one yielded finer particles of sub-mu m, via a faster size-reduction process, and exhibited better stability of dispersed particles for static annealing, suggesting the emulsifying effect of in situ formed PP-aPA graft copolymer. Both ellipsometry and transmission electron microscopy showed that the interface established in the reactive system was very thick (similar to 40 nm); it was several times the coil size of the component polymer. The thick interface is assumed to be a layer of accumulated micelles of the in situ formed graft copolymer. In the thick interface, instead of cross-hatched lamellar crystallites, long lamellar crystals were found to develop.