B2 structured single-phase (Ru,Ir)Al is synthesized directly in the ternary Ru– Al– Ir system by mechanical alloying. Complete solubility between pseudo-binary RuAl – IrAl is achieved in a composition range 10–25 at.% Ir, while the range for Al remains at 50 at.%. B2 structured (Ru, Ir) Al is formed by an abrupt reaction at the beginning of milling of all three compositions and a certain quantity of Ir was found to remain after the reaction. Further alloying and a reaction between Ir and sticking Al on the surfaces of milling tools take a much longer time and finally result in single phase B2 structured (Ru, Ir) Al. The ternary alloying element Ir has been found to ameliorate the sluggish reactivity of Ru by promoting the abrupt reaction. No decomposition process has been observed for the as-milled single-phase (Ru, Ir) Al by means of high-temperature X-ray diffraction, demonstrating the complete mutual solubility between pseudo-binary RuAl and IrAl in the present composition range. The structural evolution of as-milled materials includes reordering, strain relaxation and grain growth. The grain size of the as-milled (Ru, Ir) Al after exposure to elevated temperatures (up to 1273 K), turns out to be less than 30 nm and reflects its strong thermal stability.