A sim pie model of an electrolyte matrix for use in a phosphoric acid fuel cell (PAFC) has been proposed. It has important features in the vertical direction. Acid absorbency, bubble pressure and current density as a function of porosity and pore-size distribution were calculated. The calculated values were compared with the real values obtained from a matrix made by rolling and tape casting. The tendency of the properties in the model concurred with the real matrix. Predictions were made for the best performance. The results were a porosity of 80%, a composition having 20% of 0.01-0.1 mu m pores and 75% of 0.1-1 mu m and 5% of 1-10 mu m pores, the thickness of the matrix being 100 mu m and the particle size 1.5 mu m. It is expected that these theoretical results could be helpful in making a real matrix.