Double porous media model for mass transfer of hollow fiber hemodialyzers is presented. In the model, the hollow fiber bundle is treated as a porous region composed of two interpenetrating porous regions i.e. the blood and dialysate flow regions, and the interface of the two regions is the porous membrane through which mass transfer is performed. Navier-Stokes equations with Darcy source terms are used to describe the flows within the two regions. Modified Kedem-Katchalsky equations as other source terms are added into conservation equations to simulate the permeating flux through the porous membrane. The model is validated with respect to the experimental data in the literature. (C) 2004 Elsevier Ltd. All rights reserved.