Blends consisting of a polyamide 66 (PA) matrix (75 wt%) and a dispersed isotactic polypropylene (PP) phase were prepared by extrusion with anhydride-grafted isotactic polypropylene compatibilizers, one of high anhydride content (HAC, 2.7 wt% grafted maleic anhydride) and one of low anhydride content (LAC, 0.2 wt% grafted anhydride). HAC and LAC had similar effects on PP domain size and tensile properties at equal loadings, unlike the anhydride concentration dependency that had been reported for high PP content blends. As compatibilizer loading increased from 0 wt% to 7.5 wt%, a skin/core injection-moulded morphology gradient diminished, PP domain size decreased to less than 1 mu m, tensile strain increased and microscale deformation of the PP phase progressed from debonding to particle drawing and debonding to fibril fracture. The PP phase deformation mode depends on the interfacial strength as compared to the PP domain strength. HAC and LAC are postulated to behave similarly because of sufficient reactivity with PA and similar surface coverage by HAC-g-PA and LAC-g-PA. Interfacial strength is postulated to increase with decreasing particle size because of increasing surface/volume ratio at relatively constant surface coverage.