Phase transformations and lattice expansions of MlNi_)3.75)Co_)0.75)Mn_)0.3)Al_)0.2) during the electrochemical hydriding-dehydriding process were investigated using in-situ X-ray diffraction. An intermediate hydride γ phase between the hydrogen solid solution α phase and fully hydrided β phase can be observed during the cycling. The formation of γ phase is related to the diffusion of hydrogen in the crystal grains. The lower the charge rate is, the higher the content of γ phase is. The phase transformations during the hydriding-dehydriding process can be described as )αα+γ+ββγ+αα.) The lattice expansion from α to β is discrete, while that from γ to β is continuous. The formation of γ phase can reduce the discrete lattice expansion from α to β by 30%. Phase transformations and lattice expansions of MlNi_ 3.75) Co_) 0.75) Mn_) 0.3) Al_) 0.2) during the electrochemical hydriding-dehydriding process were investigated using in-situ X-ray diffraction The formation of γ phase is related to the diffusion of hydrogen in the crystal grains. The lower the charge rate is, the higher the content of γ phase is. The phase transformations during the hydriding-dehydriding process can be described as) αα + γ + ββγ + αα.) The lattice expansion from α to β is discrete, while that from γ to β is continuous. γ phase can reduce the discrete lattice expansion from α to β by 30%.