A kinetic Monte Carlo model is developed to simulate the oxygen reduction reaction and frequency response at the cathode of a 9 mol % yttria-stabilized zirconia fuel cell, using an asymmetrical cell scheme. To investigate the frequency-response characteristics, ac electrochemical impedance spectra have been studied with respect to variations of different electrolyte thicknesses, temperature, oxygen partial pressure, and relative permittivity of the electrolyte. Within a wide frequency range (10(3)-10(9) Hz), our results show that both electrolyte and reaction resistances are strongly temperature-dependent, with the former linearly proportional to the thickness of the electrolyte, as expected. Among the physical parameters that we studied, the temperature and the thickness of the electrolyte have the most profound influence on both the ionic current density and the ac impedance spectra of the fuel cell. The oxygen partial pressure and the relative permittivity of the electrolyte have a smaller influence on the impedance within the frequency range of this study. (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3251281] All rights reserved.