Phase equilibria in Co–Al–C ternary and Co–Ni–Al–C quaternary systems were investigated to establish the basis for designing new class of α(Co) based heat resistant alloys strengthened by the E2 1 type intermetallic compound Co 3 AlC. Phase stability of E2 1 (Co, Ni) 3 AlC was examined from the viewpoint of magnetic properties such as Curie temperature and saturation magnetization. The possibility of two-phase separation is indicated between E2 1 (E2 1 ′) (Co,Ni) 3 AlC and E2 1 (L1 2 ) (Ni,Co) 3 Al(C) in the Co–Ni–Al–C quaternary system, where we denote E2 1 ′ as standing for the ordered crystal structure of (Co,Ni) 3 AlC 0.5 formed by the extra ordering of carbon atoms. Phase diagrams information was determined by means of electron probe microanalysis and microstructural observation for the T–Al–C (T: Co, Ni, Rh, Ir) and T–Al–B (T: Rh, Ir) systems to examine the phase equilibria in each alloy system focusing on the existence of E2 1 T 3 AlC and T 3 AlB. The existence of E2 1 Ir 3 AlB (E2 1 ′ Ir 3 AlB 0.5 ) phase has been revealed in the Ir–Al–B system by diffraction analysis of transmission electron microscopy and electron probe microanalysis.