The adsorption behavior of hydrogen molecules on the calcium-decorated BC7 sheet has been investigated using first-principles calculations. Our calculations demonstrate that the van der Waals interactions are crucial for the hydrogen storage in the calcium-decorated BC7 sheet. We find that the average adsorption energy per hydrogen molecules decreases with the number of adsorbed hydrogen molecule increasing. When six hydrogen molecules adsorb, the average adsorption energy is 0.26 eV. In this case, the gravimetric density for hydrogen storage on two sides of calcium-decorated BC7 sheet is about 4.96 wt%. These features indicate that the calcium-decorated BC7 sheet has potential application in hydrogen storage. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.