Autothermal reforming (ATR), that is the combination of non-catalytic partial oxidation and adiabatic steam reforming, is an important process to produce synthesis gas (syngas) from natural gas. The main scope of this work is proposing a mathematical model considering an autothermal reformer consisting of two distinct sections; a combustion section and a catalytic bed section. in the combustion section, temperature and composition were predicted using 108 simultaneous elementary reactions considering 28 species. The results were considered as initial conditions for the catalytic bed section. A one-dimensional heterogeneous reactor model was used for kinetic simulation of the second section. Results of the model were compared by ATR process published data. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.