This paper presents newly measured electrochemical impedance spectra of two sets of nearly identical single-cell stacks except using different designs of flow distributors for planar solid oxide fuel cells (SOFCs). It is found that by using small guide vanes around the feed header of commonly used rib-channel flow distributors to improve significantly the degree of flow uniformity, values of ohmic and polarization resistances of the single-cell stack can be decreased by 32% and 60% as compared to that without using guide vanes under the same experimental conditions at 0.6V and 850 degrees C. This finding explains why by improving flow uniformity in interconnects can result in more than 10% increase of the cell power density. Moreover, the higher resistances measured for the case without using guide vanes are attributed to the anodic re-oxidation behavior due to non-uniform flow distributions in interconnects, as also verified by SEM images of anodic microstructures. These results show that the improvement of flow uniformity in flow distributors is useful to increase the performance and the longevity of planar SOFCs. (C) 2011 Elsevier B.V. All rights reserved.