Transition-metal functionalized-carbon nanotubes (CNTs) represent an important genre of hydrogen storage systems that exhibit superior storage capacity and improved storage kinetics when compared with the pristine CNTs. Here, we compare the reversible gravimetric hydrogen storage capacity of platinum-functionalized CNTs with that of pristine tubes, both measured at 300 K and an equilibrium hydrogen pressure of 1.67 MPa. The maximum reversible hydrogen storage capacity exhibited by the nano-composite material is found to be 3.2 ± 0.1 wt%, which is a nearly 50 % enhancement when compared with that of the pristine tubes. The enhanced hydrogen storage capacity of functionalized CNTs is attributed to the spill-over phenomena as suggested by the estimated storage capacity of Pt phase. The hydrogen storage in Pt nanoparticles modeled using the atomic magic number calculation and Pt hydride stoichiometry of PtH4 also suggests that nearly 15 closed shells of Pt atoms reversibly adsorb and spill hydrogen on to CNT binding sites.