Phase transformations and lattice expansions of M1Ni3.75 Co0.75 Mn0.3 Al0.2 during the electrochemical hydriding-dehydriding process were investigated using in-situ X-ray diffraction. An intermediate hydride γ phase between the hydrogen solid solution a 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 a toβ is discrete, while that from γ to β is continuous. The formation of γ phase can reduce the discrete lattice expansion from a toβ by 30 %.