Measurements of Young’s moduli at −150∼400°C and of rigidity moduli and hardness at room temperature have been carried out with Mn-Ni-Co alloys subjected to a various procedure of heat treatment and cold working. On Young’s modulus vs temperature curves, the ternary alloys slowly cooled after heating for 1 hr at 950°C showed a distinct anomalous change associatiated with the antiferromagnetic\ ightleftarrowsparamagnetic transformation. Young’s moduli at room temperature did not show a large difference by the annealed, cold worked and water quenched states and also by the alloy composition, but the temperature coefficients of Young’s moduli were greatly changed. It is to be noted that the temperature coefficients of Young’s moduli as a function of composition exhibited a large positive maximum, thus revealing the Elinvar property. The variation in rigidity modulus and its temperature coefficient with heat treatment, cold working and composition showed a close similarity to that in Young’s modulus and its temperature coefficient. The hardness is changed in a very complicated way by the heat treatment, cold working and alloy composition; the Vickers hardness is between 100 and 800. However, the corrosion resistance of Mn-Ni-Co alloys was relatively good.