The influence of the compatibilizer, a block copolymer, on the rheological behavior of polypropylene/polyamide blends is discussed here. A dual-flow behavior has been observed. At low shear rate, the blend viscosity is higher than the viscosity of the matrix, while at a high shear rate the contrary is observed. The morphology of the blends is different in the two domains, with a nodular morphology at low shear rate and a lamellar structure at high shear rate. The low shear rate behavior has been theoretically analyzed using a two-phase Oldroyd model. The copolymer has been located at the interface and is supposed to dominate the nodular dispersed-phase behavior. A good agreement has been found for the low-concentration blend. A model of lamellar flow gives the right response for the high shear rate regime. The copolymer, acting as a lubricant, has an influence on the blend viscosity and the agreement with experimental data is discussed.