NaMgH3 hydride is a potential candidate for hydrogen storage due to its high gravimetric and volumetric H densities (6 wt. % and 88 kg/m(3)). Perovskite-type NaMgH3 and Na(0.9)Ka(0).1MgH3 hydrides have been synthesized by a high-energy ball milling method in this work. The replacement of Na by 10 at.% of K results in a slight increase of lattice parameters of NaMgH3 phase and the decrease of activation energy of decomposition reactions. In comparison with NaMgH3 hydride, Na(0.9)Ka(0).1MgH3 hydride presented better dehydriding kinetic properties, the onset desorption-temperature of which is greatly decreased from 581 K to 430 K, the hydrogen-desorbed amount is about 3.0 wt. % within 6 min at 638 K, and the maximum amount is 5.25 wt. % (about 87.5% of the theoretical value) after 40 min. Further theoretical calculations, based on DFT, suggest that higher formation enthalpy and s-p-d hybridized orbitals (instead of s-p hybridized orbitals) in Na(0.9)Ka(0).1MgH3 hydride maybe contribute to the improved dehydriding properties by reducing its structure stability. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.