Porous composite solid oxide fuel cell (SOFC) electrodes formed by a mixture of electronic conductor and ionic conductor particles of small size have been studied by means of an analytical simulation model. The model takes into account electronic and ionic transport together with the electrochemical reaction, while mass transport phenomena in the macropores of the electrode have been demonstrated to be negligible. The morphological properties of the electrode have been considered with reference to percolation thresholds, in terms of effective conductivity for both phases and contact area between the phases. The results agree with the literature experimental data.Simulation shows that for thick electrodes, the optimum performance is obtained for a composition near to the percolation threshold of the electron conducting phase, while for thin electrodes the optimum performance is obtained in correspondence to the composition that ensures the maximum contact area between the two phases.The electrode thickness has to be chosen following optimisation criteria. For an electrode composition Very near to the percolation threshold of the electronic conductor the reciprocal electrode resistance shows a maximum as a function of the electrode thickness; the maximum appears for a thickness that is in the typical range for SOFC electrodes. For an electrode composition far from the percolation threshold of the electronic conductor the electrode resistance is almost constant for an electrode thickness larger than a certain value and within the typical values for SOFC electrodes.