Electrochemical reactions in solid oxide fuel cells take place around three-phase boundaries (TPBs). The electrochemically active zones (EAZs) are generated in three-dimensions around the TPBs of on-running SOFCs. This work discusses the behaviours of TPBs and EAZs via a case study on lanthanum strontium vanadate (LSV)-yttria-stabilized zirconia (YSZ) composite anode. A percolating binary particle aggregate, based on geometric random loose packing model and traditional sintering theory, is constructed to represent the LSV-YSZ anode. The TPB lengths of LSV-YSZ anodes are evaluated from the coordination numbers and sintering necks of the particles in the particle aggregate. Empirical interrelations among TPBs, EAZs, active electrode thickness, in-depth penetration of electrocatalysts of polarized LSV-YSZ anode are established. (C) 2011 Elsevier Ltd. All rights reserved.