Temperature dependences of thermal expansion, Young’s modulus and rigidity modulus, and mechanical strength at room temperature were measured with single crystals and annealed polycrystals of high elasticity alloy “Dia-flex” with the fcc structure: The alloy “Dia-flex”, composed mainly of 38.0% Co, 22.4% Fe, 16.5% Ni, 12.0% Cr, 4.0% W and 4.0% Mo showed the Young’s modulus of 23×10⁵ kg/cm², the elastic limit of 120 kg/mm² and tensile strength of 250 kg/mm² in the rolling direction. From the data obtained, the volume compressibility, principal elastic parameters, principal elastic constants, and Young’s modulus and rigidity modulus in the three principal orientations of the single crystals were calculated. The results thus obtained are as follows: the Young’s moduli at 20°C are 11.68×10⁵ kg/cm², 22.49×10⁵ kg/cm² and 33.78×10⁵ kg/cm², and the rigidity moduli at 20°C, 12.01×10⁵ kg/cm², 6.02×10⁵ kg/cm² and 5.13×10⁵ kg/cm² in the ⟨100⟩, ⟨110⟩ and ⟨111⟩ directions of the single crystals, showing a high anisotropy of the elastic moduli. The anisotropy of the temperature coefficients of elastic moduli is also very high.