The phase equilibria and the Seebeck coefficient were measured at the vicinity of the carbide (Co,M) 3 AlC (M ¼ Fe or Ni) in the Co-Al-C, Co-Fe-Al-C and Co-Ni-Al-C systems. The samples were well annealed at 1473 K and examined through X-ray diffraction measurements, energy dispersive X-ray analysis and carbon analysis. Co 3 AlC with a perovskite structure did not exist at its stoichiometric composition, but was located within a narrow compositional range near Co 3 AlC 0:67 . The maximum Seebeck coefficient was 23.3 mV/K at 873 K for Co 3 AlC 0:63 . The replacement of a small amount of Co by Fe resulted in the expansion of the single-phase area of (Co,Fe) 3 AlC x , and the Seebeck coefficient of the single phase reached its maximum, 32.6 mV/K, at 873 K and Co 3:506 Fe 0:025 AlC 0:77 in the quaternary Co-Fe-Al-C system. The addition of Ni did not stabilize this carbide, and the maximum Seebeck coefficient in the quaternary Co-Ni-Al-C system was 26.9 mV/K at 873 K.