In the present paper, ball milled LiBH4-NaBH4-MgH2 ternary-phase composite achieves nearly 100 times as much as the lithium ionic conductivity of the pristine LiBH4 at a temperature below 373 K. 4LiBH(4)-NaBH4-30%MgH2 possesses ionic conductivity of 11.2 ms cm(-1) at a temperature of 383 K, which is almost 100 times higher than that of pristine LiBH4. Furthermore, cyclic voltammetry (CV) measurements on these composite samples identified a wide potential window ranging from -1 V to 4 V, demonstrating the electrochemical stability of these samples when Li+ ions has been transported. Both X-ray diffraction (XRD) and Fourier Transform infrared spectroscopy (FTIR) results verified the structural stability of LiBH4-NaBH4-MgH2 composites during the temperature ramping process. Both phase transformation enthalpies and temperatures for LiBH4 were all reduced according to differential scanning calorimetry (DSC) measurements, implying that the high temperature phase of LiBH4 could be effectively stabilized by co-additives of NaBH4-MgH2.