A composite electrode comprising a porous mixture of solid electrolyte (typically yttria stabilized zirconia, YSZ) and electronically conducting, electrocatalytic material (typically strontium doped lanthanum manganite, LSM) is generally used to improve the cathodic performance of the solid oxide fuel cell (SOFC). The advantage of the composite electrode is that the reaction zone is spread from the electrode/electrolyte interface into the electrode, effectively resulting in a functionally diffuse interface where the charge transfer reaction occurs. The present study proposes a one-dimensional dc and ac model that takes into account mass and charge conservation, transport of species and reaction kinetics. It considers the porous electrode to be a homogeneous medium characterized by a number of parameters, and in particular ionic conductivity and the diffusion coefficient. The influence of kinetic and transport parameters as well as that of the microstructure on the shape of both polarization curves and impedance diagrams is discussed.