In a previous paper, it was demonstrated that a MgH 2 –NaAlH 4 composite system had improved dehydrogenation performance compared with as-milled pure NaAlH 4 and pure MgH 2 alone. The purpose of the present study was to investigate the hydrogen storage properties of the MgH 2 –NaAlH 4 composite in the presence of TiF 3 . 10 wt.% TiF 3 was added to the MgH 2 –NaAlH 4 mixture, and its catalytic effects were investigated. The reaction mechanism and the hydrogen storage properties were studied by X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry (DSC), temperature-programmed-desorption and isothermal sorption measurements. The DSC results show that MgH 2 –NaAlH 4 composite milled with 10 wt.% TiF 3 had lower dehydrogenation temperatures, by 100, 73, 30, and 25 °C, respectively, for each step in the four-step dehydrogenation process compared to the neat MgH 2 –NaAlH 4 composite. Kinetic desorption results show that the MgH 2 –NaAlH 4 –TiF 3 composite released about 2.4 wt.% hydrogen within 10 min at 300 °C, while the neat MgH 2 –NaAlH 4 sample only released less than 1.0 wt.% hydrogen under the same conditions. From the Kissinger plot, the apparent activation energy, E A , for the decomposition of MgH 2 , NaMgH 3 , and NaH in the MgH 2 –NaAlH 4 –TiF 3 composite was reduced to 71, 104, and 124 kJ/mol, respectively, compared with 148, 142, and 138 kJ/mol in the neat MgH 2 –NaAlH 4 composite. The high catalytic activity of TiF 3 is associated with in situ formation of a microcrystalline intermetallic Ti–Al phase from TiF 3 and NaAlH 4 during ball milling or the dehydrogenation process. Once formed, the Ti–Al phase acts as a real catalyst in the MgH 2 –NaAlH 4 –TiF 3 composite system.