In this study, a three-dimensional, steady state model has been developed for a single planar solid acid fuel cell (SAFC) with CsH2PO4-MOA composite electrolyte. The model considers all of the fuel cell components (flow channels, gas diffusion layers, catalyst layers, and electrolyte). This model describes the electrochemical reactions on the active areas of the anode and cathode electrodes, and transport phenomena that occurring in each part of the fuel cell consisting of, fluid flow in flow channels, diffusion of reactants in gas diffusion layers (porous medias), and ions transport within the electrolyte. The model is solved in a 3D environment using COMSOL MULTIPHYSICS software. Finally the model results validated by the experimental data (current density-voltage graph). The advantage of this model is the prediction of the SAFC behavior in different operational conditions. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.