It is desired to develop computational procedures to simulate internal current density, anode/cathode gas concentrations, and temperature distribution in solid oxide fuel cell (SOFC) systems. In this study, the influences of various operational conditions on the exchange current density, the essential parameter to simulate SOFC performance, are revealed and discussed. The anodic exchange current density depended strongly on the humidity of H 2-based fuel gas, and it exhibited the highest value at around 40% H 2O. The cathodic exchange current density was strongly affected by the operational temperature. Parameters necessary to describe dependencies of exchange current density on various operational parameters were determined by fitting measured exchange current density values with empirical equations.