Micro powder injection molding (mu PIM) differs from conventional powder injection molding (PIM) with respect to the effects of the mold dimensions. In this study, the theological properties of the feedstock (mixture of carbonyl iron powders and binder) in molds with different diameters were analyzed by numerical simulation based on the powder-binder two fluid model. Viscosity, temperature, shear strain rate, velocity and the flow distance of the feedstock varied for different molds. but did not just reduce by proportion when the mold was smaller which would lead to many defects in green parts. The inner wall of the mold that was the key factor influencing the filling step in mu PIM needed more studies. (C) 2009 Elsevier B.V. All rights reserved.