The effect of potassium as a promoter on the activity of Pt/CeO2 catalysts for hydrogen production from ethanol was studied in this work. The Pt/CeO2 catalysts with or without potassium were prepared with incipient impregnation method and analyzed using synchrotron-based X-ray diffraction (XRD), X-ray absorption near-edge spectroscopy (XANES), oxygen adsorption, ethanol temperature programmed desorption (TPD) NH3-TPD, and TPR. We find that Pt particles on all CeO2-based catalysts were less than 2 nm. Potassium addition did not have benefit on hydrogen production activity. However, potassium modified active sites, acidity, and interaction between Pt and CeO2. Oxygen storage capacity (OSC) was decreased, while the acidity was neutralized and the interaction between Pt and CeO2 was weakened when potassium was added to Pt/CeO2. Potassium promoted ethanol decomposition reaction while inhibited decarbonylation of acetaldehyde and CH4 formation. This work confirms our previous finding that Pt-CeO2 synergistic interaction played an important role for hydrogen production from bio-alcohols. Copyright (c) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.