Particle-filled preceramic polymer injection into woven fiber preforms is currently under investigation as a means of processing dense, complex-shaped ceramic composites. The distribution of filler particles as a result of filtration during their impregnation into dense fiber preforms, has a crucial effect on the properties of the end product. In general, highly filtered particle distributions are not desirable since they lead to nonhomogeneous part microstructure and hence, mechanical properties of the composite. In order to understand how various process parameters (injection velocity, inlet particle concentration, fiber preform permeability, etc.) interact during impregnation and to ultimately control the amount of filtration, a process model is presented. A multi-dimensional, transient particle filtration formulation is coupled with isothermal, anisotropic Darcy’s flow to predict filler concentration profiles during molding of complex shapes. The permeability of the preform, porosity of the flow domain, viscosity of the impregnating resin and filtration coefficient are all affected by the particle deposition and they constitute the nonlinearity in the coupled flow and filtration equations. Results for 2-D impregnation into complex preforms are presented and methods for manipulating particle distribution are discussed.