The objective of the present work is to study the linear and non-linear viscoelastic behavior of molten polypropylene filled with ferrite particles at different concentrations. Formulation, rheology and process interplay as a whole matter in this study. The effect of adding a commercial dispersant on the flow properties has been investigated by rotational and capillary rheometer. In rotational rheometry, an accurate study about structural material changes can be performed, while, in capillary rheometry the material is subjected near to real processing conditions and thus its non-linear behavior can be investigated. In rotational rheometry, a pre-shear was applied (1s^-1 for 160 s) and was followed by a time sweep experiment (w=1rad/s) at different deformations. The measurement of G’ and G” over time showed that such materials were not stable, so that the composite structure changed a lot over time. Interparticle interactions together with a slight sedimentation effect might be the origin of this effect. It has been observed that particles can reorganize into a network under dynamic and quiescent conditions and thus a gel point can be determined. Adding a dispersant to these formulations stabilizes the morphology and thus the moduli and the viscosity remain constant over time. In capillary rheometry, two process windows were investigated: extrusion window (10^0 to 10^2 s^-1) and injection moulding window (10^2 to 10^5 s^-1). No evolution of the structure has been observed in capillary rheometry. The effect of adding a dispersant on the flow properties is more visible in the dynamic state than in the steady state. In the extrusion window, the addition of the dispersant agent decreases the inter-particle interactions and thus a decrease in viscosity is observed. Nevertheless in the injection molding window, no change in viscosity was perceived. Wall slip phenomenon may be the origin of this hide effect.