This paper is a report of the results of investigations on the phase equilibria among γ (Al), and γ′ (L12) and β(B2) phases, β → β′ (L10) martensitic transformation temperatures, and microstructural features of multi-phase alloys fabricated through various thermo-mechanical processes in the Ni-Co-Al system. The isothermal section diagrams and tie line configurations of 900, 1100 and 1300°C was determined by energy dispersion X-ray spectrometry (EDX) analysis. The Ms temperature was measured by differential scanning calorimetry (DSC) analysis and a contour of iso-Ms composition lines was determined. On the basis of this information, the various types of microstructure of β + γ, β + γ′ and β + γ + γ′ phases was obtained through thermo-mechanical treatment. Morphological features of the multi-phase alloys with fine blocky, plate, Widmanstätten and lamellar structures was discussed in connection with heat-treatment, phase diagram and martensitic transformation. Mechanical properties were also examined and a good combination of strength and ductility was obtained in the multi-phase alloys.