In this work the transient shear behaviour, in terms of both flow and stress relaxation, were measured for several blends of PA6/EPM/EPM-g-MA. The results indicate that there is a competition between slip at the interface due to the non-compatibility between the PA6 and the EPM and the action of the compatibilizer. In flow experiments, at low total strains it was observed that the behaviour is characteristic of immiscible polymer blends and gradually changes to that typical of compatible blends. This suggests that initially the action of the compatibilizer (especially for low compatibilizer contents) is not enough to prevent the lower viscosity PA matrix from slipping around the high viscosity EPM droplets. However, as the droplets are deformed and oriented, the increase in interfacial area enhances the performance of the compatibilizer, thus resulting in a much better interaction between the two phases across the interface.