A theoretical model was developed to study the electrical characteristics of a solid oxide steam electrolyzer (SOSE) for hydrogen production. The activation and concentration overpotentials at the electrodes as well as the ohmic overpotential at the electrolyte were considered as the main sources of voltage loss. The Butler-Volmer equation, Fick's model, and Ohm's law were applied to characterize the overpotentials. The theoretical model was validated as the simulation results agreed well with the experimental data from the literature. In the study of the component thickness effect, anode-support SOSE configuration was identified as the most favorable design. Further parametric analyses were performed to study the effects of material properties and operating conditions on the anode-supported SOSE cell performance. The results have shown that increasing electrode porosity and pore size can reduce the voltage loss. In the operation, both temperature and steam molar fraction can be increased to enhance the SOSE electrical efficiency. The pressure should be regulated depending on the current density. The electrochemistry model can be used to perform more analyses to gain insightful understanding of the SOSE hydrogen production principles and to optimize the SOSE cell and system designs. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.