Density of electrochemically active triple phase boundary sites is one of the most important factors that affect the performance of composite cathodes in Solid oxide fuel cells. Only the topologically connected triple phase boundaries can become electrochemically active. Therefore, microstructure-based geometric modeling of topologically connected triple phase boundaries is of interest. In this contribution, three-dimensional microstructure simulations are utilized to predict the topological connectivity of the triple phase boundaries in a composite SOFC cathode as a function of the volume fractions of the constituents, particle size, shape, and the thickness of the cathode. The simulations show that the volume fractions of the constituent phases and electrode thickness are the most important factors that affect the topological connectivity. The simulations also reveal the geometric conditions under which most of the triple phase boundaries are topologically connected, so that for such SOFC cathode microstructures, the existing models for total geometric triple phase boundary length density can be also used to approximate the length density of the topologically connected triple phase boundaries. (C) 2012 Elsevier B.V. All rights reserved.