We studied hydrogen storage properties of Ca-decorated a novel boron sheet through first principles calculations. It was found that up to six H-2 molecules can be captured by a Ca atom at 0 K with an average binding energy in a better range of -0.20 to -0.32 eV/H-2. The gravimetric hydrogen density of 12.68 wt.% is reached when Ca is adsorbed on both sides of the boron sheet. The mechanism for binding the attached H-2 molecules comes from not only the polarization mechanism but also the orbital hybridization. The effect of temperature and pressure on hydrogen storage performance of the Ca-decorated boron sheet was also evaluated. At room temperature, all the hydrogen adsorbed structures are stable at mild pressure. Our results indicate that Ca-decorated boron sheet is a potential hydrogen storage medium for on-board vehicle application. Copyright (C) 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.