The ohmic resistance of anode-supported solid oxide fuel cells (SOFCs) having a manganese-based cathode was lowered when operated in synthetic coal gas containing hydrogen chloride. This effect was not observed for cells with cathodes that did not contain manganese. Substantial amounts of Mn were found throughout the grain boundaries of the 8 mol % yttria-stabilized zirconia electrolyte. Exposure to HCl partially removed Mn near the anode/electrolyte interface, presumably by volatilization as MnCl2(g). This work suggests that one of the underlying causes of the higher than expected electrolyte resistance in anode-supported SOFCs involves the formation of a Mn-containing insulating layer at grain boundaries. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3380668] All rights reserved.