Catalytic hydrogen-oxygen reaction is a potentially effective way to help start up proton exchange membrane fuel cells (PEMFCs) from sub-zero temperatures. In this study, the anode hydrogen-oxygen catalytic reaction is implemented in a three-dimensional multiphase cold start model. It is found that successful cold start from -20 degrees C can be achieved with the assist of the catalytic reaction in galvanostatic mode. With anode catalytic reaction, the start-up current density must be moderate, because a high current density lowers the assisted heating effect, and a low current density slows down the start-up process. The temperature difference between the anode and cathode catalyst layers (CLs) is negligible, which indicates that the heating location in the electrodes for the catalytic reaction makes no significant difference. The humidification of anode due to the catalytic reaction also reduces the ohmic resistance of the membrane, leading to enhanced performance during the start-up processes. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.