Abstract: A series of Li_2-xMn_1-xGa_xCl₄ (x=0, 0.1, 0.3, and 0.5) materials were synthesized with the mechanochemical approach. As confirmed by X-ray powder diffraction and Rietveld refinements, Ga³⁺can be successfully incorporated into the octahedral sites that are partially occupied by Mn²⁺.The as-milled materials with relatively low crystallinity generally exhibit higher ionic conductivity than the well crystallized ones produced by annealing at 250 ℃. Among all the materials studied,the as-milled Li_1.9Mn_0.9Ga_0.1Cl₄shows the highest ionic conductivity (8.3×10^-5 S·cm^-1), which is two orders of magnitude higher than that of the as-milled Li₂MnCl₄(7.12×10^-7 S·cm^-1). While the unit cell volume does not vary significantly with the composition, the appropriate Li vacancy content should play an important role in the optimized ionic conductivity of Li_1.9Mn_0.9Ga_0.1Cl₄.