Modeling an electrode in solid oxide fuel cells (SOFCs) as two finite layers is numerically investigated. A simulation is conducted using the developed mathematical model, wherein an SOFC electrode is considered as a porous composite structure of electron- and ion-conducting particles. Moreover, an electrochemical reaction is considered to occur throughout the electrode. In other words, an electrode is treated as a reaction zone layer having triple phase boundaries (TPBs) scattered throughout the electrode, consistent with the micro modeling approach of treating electrodes. The model takes into account the transport of multi-component mixture in an electrode together with electrochemical reaction, the transport of electrons and ions in the respective electron-conducting and ion-conducting particles of the electrode. It is found that both the dimensionless electronic and ionic current densities remain constant with respective values of one and zero for most part of the anode before started to vary towards the end of the anode. Further, from the distributions of dimensionless electronic and ionic current densities in the anode, it can be deduced that the part of the anode (electrode) where the value of dimensionless electronic current density is one, can be considered as an electron-conducting (ion insulator) layer, referred to as the anode (electrode) backing layer; the part of the anode (electrode), where there is a variation in the electronic and ionic current densities and electrochemical reaction rate is most effective, can be considered as a mixed-conducting layer, referred to as the reaction zone layer. Finally, a parametric study is conducted to investigate the effect of key operating and design conditions on the thickness of the reaction zone layer in an SOFC anode. (C) 2009 Published by Elsevier Ltd on behalf of International Association for Hydrogen Energy.