Our experimental data from a capillary rheometer clearly show that powder/binder mixtures for powder injection molding (PIM) experience so-called slip phenomena at the wall, like many particle-filled materials. It is thus of great importance to characterize quantitatively the slip, together with shear-thinning viscosity data of power/binder mixtures in view of proper numerical simulations of the PIM filling process. The slip at the wall could be quantified in terms of a slip velocity or in terms of a very thin slip layer. The present paper adopted the well-known Mooney’s method for determining slip velocity, whereas the slip layer thickness was determined by a newly-proposed method. The dip velocity, or the slip layer thickness, thus determined were then introduced into the finite element analysis of the PIM filling process. This was found to have a significant effect on the overall flow behavior during the injection molding filling.