Particle capture at porous media in cross-flow microfiltration is studied to investigate permeability reduction as a function of membrane pore size and particle size distribution. A new model in pore scale and its pertinent mathematical expressions, which consider pore and particle size distribution, are provided. Permeability reduction of the membrane because of size exclusion during particulate suspension flow was predicted using the developed model. It is assumed that the size exclusion is the dominant mechanism of particle retention causes pore blocking and permeability reduction in the porous media. The exact analytical solution of the stochastic model for size exclusion is used to develop a new mathematical expression with minimal number of parameters (alpha alpha, beta beta, and eta eta) to estimate permeability reduction of the porous media as a function of time, pore size distribution of the membrane and particle size distribution of the injected suspension. Reasonable agreement between the predicted values based on the proposed model and the published laboratory results was achieved. (C) 2013 Elsevier B.V. All rights reserved.