The processes that occur during the deformation of nylon 6/polypropylene blends modified with maleated rubbers were identified by dilatometric measurements and electron microscopy. These toughening mechanisms were found to depend on the type of rubber used as modifier (ethylene-propylene random copolymer, EPR-g-maleic anhydride (MA), or styrene-ethylene/butylene-styrene triblock copolymer, SEBS-g-MA), and on the relative ratio of nylon 6 to polypropylene (PP) in the blend. Blends based on EPR-g-MA showed significant volume dilation during deformation in a low strain rate tensile test. Electron microscopy techniques revealed that the main dilational mechanism in these blends is cavitation of the rubber dispersed as particles in the nylon 6 phase and at the nylon 6/PP interface. Similar results were obtained for specimens deformed in a high speed impact test. Except for one composition, nylon 6/PP blends modified with SEBS-g-MA showed negligible changes in volume during slow tensile deformation, and no indication of dilational processes (as determined by electron microscopy) was found in broken specimens deformed under notched Izod impact conditions. However, cavitation of the rubber particles was observed in 80/20 nylon 6/SEBS-g-MA blends deformed in the high speed impact test. This indicates that under appropriate stress and strain conditions, cavitation of SEBS-g-MA particles can occur. The structure and properties of the rubber and its particle size are factors that contribute to the differences in the extent of cavitation of nylon 6/PP blends modified with SEBS-g-MA or EPR-g-MA.