PURPOSE: To obtain a heat-resistant Fe-Ni alloy with high toughness and strength by specifying a composition consisting of C, Si, Mn, Ni, Cr, Ti, Al, B, Ca and Fe.

CONSTITUTION: This heat-resistant Fe-Ni alloy with high strength consists of, by weight, 0.01W0.2% C, ≤2% Mn, 25W50% Ni, 13W23% Cr, 1.5W3.5% Ti, 0.1W 0.7% Al, 0.001W0.05% B, 0.001W0.1% Ca and the balance Fe with inevitable impurities or further contains 0.003W0.05% N and one or more among 0.005W 0.05% Zr, 0.05W1% V, 0.05W3% Nb+Ta, 0.05W3% Mo and 0.05W3% W. The alloy is obtd. by subjecting an alloy having said composition to proper heat treatment so as to accelerate the precipitation of γ'-phase [Ni3(Al, Ti)] in the grains and to inhibit the precipitation of η-phase [Ni3Ti] which deteriorates the toughness.