We report that potassium aluminum tetrahydride, KAlH 4 , exhibits a rapid reversible hydrogen decomposition reaction without any aid of external catalysts. This is significantly different from the reaction mechanism of NaAlH 4 and LiAlH 4 , in which the homogeneous doping of the transition metal catalyst is essential for the reversibility and fast kinetics. The reversible dehydrogenation and hydrogenation were clearly observed without a catalyst over a temperature range 250-340 o C under <10 bar of hydrogen. Hydrogen storage ability was above 3.5 wt.% (81.4% of the theoretical value of 4.2 wt.%). KAlH 4 may be a competitive option with a lightweight but high-temperature metal hydride system such as Mg 2 NiH 4 . These findings will also provide renewed guidelines for understanding the reaction mechanism of the catalyzed alanates as reversible hydrogen storage materials.