Applying first principles electronic structure calculations and molecular dynamics (MD) simulations we have studied the structural stability, hydrogen adsorption capability and hydrogen desorption kinetics of Y-decorated single walled carbon nanotube (SWCNT). We have predicted that a single Y atom attached on SWCNT can physisorb up to six hydrogen molecules which is not reported so far. Our MD simulations with four Y atoms placed at the alternate hexagons of SWCNT showed no clustering effect of Y atoms at room temperature and also we found that the system is stable even at higher temperature (700 K). For the first time we showed that 100% desorption at comparatively lower temperature can be achieved in a transition metal-decorated SWCNT system. Therefore the Y-decorated SWCNT has the potential to become a promising hydrogen storage device.