The positive temperature dependence of strength was confirmed by means of compression tests in Ll2 ordered alloys which had been newly added to the group of those exhibiting a positive strength behavior in hot hardness tests in previous work. Those were Pt3In, Pt3Sn, Pd3Pb, Fe3Ga, Pt3Ti, Pt3Cr, Pd4Ti, and Zr3In. Moreover, Pt3Al, Pt3Ga and Pt4Sb were added to the group of anomalous compouds in this study. The activation constants were derived from a modified model based on the thermally activated model proposed by Liang and Pope.From the relationships among the derived activation constant, the apparent atomic radius ratio and the electron concentration for platinum- and nickel-based alloys, it was deduced that the Ll2 phase tends to be destabilized with respect to the DO22 phase before the DO19 phase becomes stable as the relative atomic radius of the B-subgroup element minority component in A3B alloys is increased. It was also shown that 4B-subgroup elements make the Ll2 phase of A3B alloys less stable than 3B-subgroup elements as one of the components. It was confirmed that the lower phase stability of the Ll2 phase with respect to the DO22 phase is responsible for the anomalous strength behavior. This conclusion is consistent with the thermally activated cross slip model.From this result it was proposed that a systematic variation in phase stability can be achieved by the partial replacement of one of the elements in an alloy in either direction, according to whether the atomic radius or electron concentration is to be increased or decreased.