Abstract: The effect of hydrogen on nanoindentation creep at room temperature and plastic deformation of nanoindentation in preferentially orientated polycrystalline Ni₅₀Mn₃₀Ga₂₀ was investigated by nanoindentation. The results show that nanoindentation creep in the preferentially orientated polycrystalline Ni₅₀Mn₃₀Ga₂₀ could occur at room temperature. After the specimens was hydrogen charged in vacuum at room temperature, the introduced hydrogen could not only promote the nanoindentation creep, but also release the elastic energy stored in martensitic pseudoelastieity and induce reversible martensitic transformation, which resulted in the partial recovery of plastic deformation.