One important advantage of MCFCs is the possibility of using different fuel gases (natural gas, coal gas, biogas, landfill gas, etc.). However, these fuels contain impurities that can damage MCFCs, and, of these, sulphur compounds seem to be the most harmful, even at low concentrations. The aim of this work is to test the effect of different H2S compositions on operating variables, investigate the relationships, propose phenomena reading and obtain new information to define tolerance limits. In particular, chemical, electrochemical and physical poisoning mechanisms were taken into account, trying to evaluate their importance studying the effects of exposure time, temperature and current density on MCFC performance when H2S polluted anodic gas is fed. To support the investigation, experimental tests were performed at the Fuel Cell Research Center laboratories of KIST (South Korea) and a theoretical analysis was also proposed to suggest operating strategies, for example showing how high current density or temperature values can emphasize the negative effect of poisoning. The results obtained gave new suggestions for approaching data interpretation, confirming the possibility of using MCFCs when a number of ppm of H2S is present in the feeding fuel. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.