Binary blends of polyamide 6 (PA-6) and the copolymer styrene-maleic anhydride (SMA) have been prepared via melt extrusion. The amino end groups of PA-6 and the anhydride groups of SMA react with each other during melt blending; this leads to the formation of a comblike graft copolymer at the interface between PA-6 and SMA. The aim of this paper is to investigate in detail the factors affecting the graft copolymer formation. An extraction procedure has been developed to remove the PA-6 phase from the blends, and the remaining SMA phase has been analyzed with FTIR to determine the amount of reacted anhydride groups. Several material parameters such as the M-w of PA-6, the MA content of SMA, and the amount of dispersed phase were varied to get a better insight into the graft copolymer formation. It was found that the number of grafted Ph-6 chains per SMA chain is not much limited by conformational restraints; very complex graft copolymers can be formed. On the other hand, it was found that the concentration of amino end groups of PA-6 is a crucial parameter with respect to the chain microstructure of the graft copolymer formed. The amount of generated interfacial area between the immiscible phases is also an important parameter for the reaction extent. Calculations were made for estimating the thickness of the interfacial zone in these reactively compatibilized blends; these calculations are based on the FTIR data, the dispersed-phase particle size, and model assumptions. Finally, the relation between the MA content of SMA as reactive compatibilizer and the particle size of the PA-6/SMA blend was investigated.