The promotion effects of Ca on catalytic performance of Ca-doped Pt/Al2O3 catalyst were investigated by varying Ca content and impregnation orders. The Ca-doped Pt/Al2O3 catalyst with atomic rate Ca/Pt = 5 exhibited the highest catalytic activity and stability. Detailed analyses show that low Ca content (Ca/Pt < 5) could not efficiently promote hydrogen spillover from Pt-Al interface to the support and reduce the strong acid sites on the support. However, high Ca content (Ca/Pt > 5) decreases the initial activity due to the coverage of Ca on the support and increases the amount of Pt strongly interacting with Ca, which inhibits Pt reduction. Furthermore, the Ca promotion effect is more pronounced when Ca is added prior to Pt due to surface modification of Ca on Al2O3 support. This modified catalyst possesses more dispersed Pt, lower acidity and larger amount of spilled-over hydrogen. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.