In this work, hydrogen storage properties and reaction mechanism of NaAlH4-Mg(BH4)(2) (2:1) composites system with and without additive have been investigated. The secondaryhydride system was found to initiate a transformation of the NaAlH4/Mg(BH4)(2) to Mg(AlH4)(2)/NaBH4 during ball milling, and there was a mutual destabilization among the hydrides. Three major dehydrogenation steps were observed in the systems, which corresponded to the decomposition of Mg(AlH4)(2), MgH2, and NaBH4. Temperatureprogrammed desorption results showed that the TiF3-doped NaAlH4-Mg(BH4)(2) (2:1) composite sample started to release hydrogen at about 75 degrees C, which was 60 degrees C lower than that of undoped NaAlH4-Mg(BH4)(2) (2:1) composite sample. In addition, the reaction pathway of the NaAlH4-Mg(BH4)(2) (2:1) composite system, and the mechanisms that worked in this composite during the de/rehydrogenation process were determined by X-ray diffraction. The Kissinger analysis has shown that the apparent activation energy, E-A, for decomposition of NaBH4 in the NaAlH4-Mg(BH4)(2)-TiF3 composite reduced to 139.85 kJ/mol compared with 155.73 kJ/mol in NaAlH4-Mg(BH4)(2) composite. It is believed that the enhancement of the de/rehydrogenation properties of undoped NaAlH4/Mg(BH4)(2) was attributed to the formation of intermediate compounds, including Mg-Al and Mg-Al-B alloys, upon dehydrogenation, which changed the thermodynamics of the reactions by altering the de/rehydrogenation pathway. Meanwhile, as for the doped sample, the TiF3 component played a catalytic role through the formation of Ti-containing and F-containing catalytic species, which might have promoted the interaction of Mg(AlH4)(2) and NaBH4, and thus, further improved the dehydrogenation of the NaAlH4-Mg(BH4)(2) (2:1) system. Copyright (c) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.