A preliminary study on the phase relations in Al-Mo-Ti-X quaternary systems in the vicinity of Ti-trialuminide phases is carried out with various additives X= Mn, Cr, Fe, Ni and Ag. 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 it equilibrates with a DO22-Al3Ti phase containing a large amount of Mo. It is found that, by additions of X= Mn, Cr, Fe or Ni, an L12-(Al, X)3 Ti phase appears near the two-phase region composed of the DO22-Al3 Ti and bcc phases in the Al-Mo-Ti ternary system. By heat treatment at 1223 K, the bcc phase of quaternary alloys decomposes into the A15-Mo3Al, DO22, L12 and/or σ phases, and no voids are observed. The mechanical properties of these alloys are also investigated by Vickers hardness.