The capacity of hydrogen adsorption of magnesium (Mg) decorated small boron (B) clusters (Mg2Bn; n = 4-14) was studied using density functional theory (DFT). The calculated results indicate that H-2 adsorbed in the molecular form. The Bader's topological analysis indicates the presence of closed shell type interaction between clusters and H-2 molecules. The clusters are stable even after the adsorption of H-2 molecules. The average energy of H-2 adsorption is calculated to be in the range of 0.13-0.22 eV/H-2. The Mg2B6 cluster shows maximum H-2 adsorption (8.10 wt%) at ambient temperature and pressure. Further, we have performed molecular dynamic (MD) simulation at room temperature for each cluster to understand adsorption and desorption of H-2 molecules with time. The MD simulation revealed that most of the adsorbed H-2 molecules moved away from the clusters within 200 fs. However, one H-2 molecule remains attached with the Mg(2)B(11 )cluster even after 200 fs. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.