In the Al-Mo-Ti ternary system, a bcc-phase field extends from the Ti-Mo edge to high-Al region at high temperatures, and at low temperature the low Ti region is replaced partially by a two-phase region composed of an A15-Mo3Al and a D022-Al3Ti phases. It enables us to form a fine lamellar structure. Besides, most of the Ll2-trialuminides stabilizing elements also act as the bcc-βTi phase stabilizer. So, the designing of the bcc-Ll2 two-phase alloys also can be expected by adding them to the Al-Mo-Ti alloys. In order to apply such ideas for microstructural control, a series of studies on the phase relations in the Al-Mo-Ti-X quaternary systems have been carried out to introduce an Ll2-(Al,X)3Ti phase and/or bcc phase for ductile-phase toughening. It is found that, by additions of X = Cr, an Ll2-(Al,Cr)3Ti phase appears near the two-phase region composed of the D022-Al3Ti and bcc phases. By heat treatments, the D022-Al3Ti and/or Ll2-(Al,Cr)3Ti phases precipitates from the bcc phase, and no voids are observed. The mechanical properties of these alloys are also investigated by Vickers indentation tests.