Powder Injection Molding (PIM) is a process by which plastic injection molding equipment is used to mold polymeric feedstocks that are heavily filled with metal or ceramic powders into green parts, which are subsequently debound and sintered into metal or ceramic parts. Feedstock formulations commonly recommend the addition of metal stearates to improve processability, but the effects of adding stearates are not well documented. This study investigates the effects of adding metal stearates to a PIM feedstock prepared with a wax-based binder system and silicon. Aluminum stearate and calcium stearate were incorporated at varying weight percentages while keeping the silicon powder fraction constant. Rheological properties were characterized on a parallel plate rheometer to compare yield stress and zero-shear viscosity. Predictive viscosity models were also developed for each feedstock using a cone and plate rheometer. Finally, samples were molded from each feedstock to evaluate flow behavior at molding conditions as well as final part properties. The results show that aluminum stearate significantly lowered the yield stress of the feedstock, while calcium stearate had the reverse effect.