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The elastic stiffnesses of 11 single crystals of β2‐NiAl containing 47.6 to 60.5 at % Ni are determined between —196 and 400 °C. The shear stiffness C′ = (C11 – C12)/2 decreases strongly and its temperature coefficient becomes positive with increasing Ni concentration. C44 and CL = (C11 + C12 + C44)/2 decrease markedly if the Ni concentration falls below the stoichiometric composition. The results are discussed in terms of lattice softening due to ionic repulsion, the reduction in stiffness due to structural vacancies and effects of low temperature structural transformations.

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