Abstract: A numerical model was presented to predict the specific proton conductivity of the catalyst layer in Proton Exchange Membrane Fuel Cells (PEMFC).This model was derived from the random packed spheres with simple cubic, body-centered cubic and face-centered cubic structures.The effects of sphere radius r_s, bulk proton conductivity k_b, contact parameter γ and contact angle α on proton transfer within a homogeneous agglomerate sphere consisting of carbon-supported catalyst and electrolyte were analyzed.A correlation equation of specific proton conductivity was obtained by data fitting.The real effective proton conductivity in the catalyst layer was measured by addition to a standard Membrane Electrolyte Assembly of an inactive composite layer in the electrolyte path between the anode and cathode. The model was validated by good agreement between calculations and measured data.