[en] The phase equilibria, A2/B2 and B2/L2₁ (or D0₃) order-disorder transitions and martensitic transformation on the Ni-Fe side of the Ni-Fe-Ga system were examined by electron probe microanalysis (EPMA) and differential scanning calorimetric (DSC) measurement. The equilibrium compositions of interrelations mainly among the α (A2), β (B2), β' (L2₁ or D0₃), γ (A1) and γ' (L1₂) phases were determined using diffusion triples which were fabricated by two-step diffusion coupling. It was confirmed that a bcc single-phase region composed of α, β and β' at 850-1000 deg. C exists in a wide composition range and that the critical temperature of the B2/L2₁ order-disorder transformation in the Fe₃Ga-Ni₃Ga pseudo-binary section gradually increases with increasing Ni content. The existing composition region of the martensite phase at room temperature was also determined by the diffusion triple method