An impedance separation analysis of the anode and cathode of a practical solid oxide fuel cell (SOFC) is conducted. Electro-chemical impedance spectroscopy with a two-electrode setup is applied to an anode-supported intermediate temperature microtubular SOFC composed of a Ni/(ZrO2)(0.9)(Y2O3)(0.1) cermet anode, a La0.8Sr0.2Ga0.8Mg0.2O2.8 electrolyte, and a (La0.6Sr0.4) (Co0.2Fe0.8) O-3 cathode. Measurements are carried out for the cell operated at 700 degrees C with varying flow rates and compositions of the H-2/N-2 mixture gas fed into the anode and the O-2/N-2 mixture gas fed into the cathode. The anode and cathode impedances are thereby separately assigned to low and high frequency impedance spectra, respectively. An equivalent circuit model is applied to the spectra to acquire the polarization resistances and associated capacitances for the charge and mass transfer processes at the anode and cathode and the cell ohmic resistance. The variation in these circuit parameters are then obtained in accordance with current densities and anode gas-feed conditions. In addition, the hydrogen diffusion length correlated with the Nernst loss in the axial direction of the anode substrate tube is estimated. These parameters obtained separately and simultaneously for each part of the cell are informative for a detailed analysis and diagnosis of practical SOFCs under operation. (c) 2010 The Electrochemical Society. [DOI: 10.1149/1.3486805] All rights reserved.