A systematic investigation is carried out on the temperature dependence of strength in ternary Ni₃Al compounds with additions of transition metal elements. The rate of solid solution hardening per one atomic percent of the solute, dσ⁄dc, is determined for each of the ternary addition using the compressive flow stress measured at liquid nitrogen temperature. It is found that dσd⁄dc can not be simply correlated with the rate of lattice parameter change, da⁄dc, although a linear correlation has been found for the addition of B-subgroup elements. The rate of change in activation energy to provide the anomalous positive temperature dependence of strength per one atomic percent of the solute, dU⁄dc, is then evaluated. Together with the results for the addition of B-subgroup elements, the apparent valence is assigned for each transition metal element by an analogy utilizing equi-valence contour determined for B-subgroup elements. Then it becomes possible to discuss the relative magnitude of the mechanical anomaly in Ni₃Al in terms of the phase stability concept of L1₂ phase, in which e⁄a ratio as well as the atomic radius ratio of the compound, R_B⁄R_A, as affected by ternary addition is an important parameter to alter the stability of the phase against other geometrically close packed phases.