Abstract: The Fe-Co-Ni based superalloys (Fe₁₈Ni₂₃Co₂₅Cr₂₁Mo₈WNbC₂) were prepared by the hot isostatic pressing (HIP), using the gas atomization powders as the raw material, and the effects of HIP temperatures on the microstructure, mechanical properties, and fracture morphology of the densified Fe₁₈Ni₂₃Co₂₅Cr₂₁Mo₈WNbC₂ superalloys were studied. The results show that, the HIPed superalloys have the high densification degree, and the sintered superalloys are composed of the (Fe, Ni) solidsolution phase and the dispersed M6C carbide strengthening phase. With the increase of sintering temperature from 950 ℃ to 1050 ℃, the density and mechanical properties of the HIPed sintered superalloys increase. When the HIP temperature reaches 1100 ℃, the grains of the densified sintered superalloys grow significantly and the mechanical tensile properties decrease. The tensile fracture of the densified sintered superalloys at room-temperature is mainly transgranular, and the grains in the local area are stretched and cracked. The tensile fracture of the densified sintered superalloys at 650 ℃ is a mixture of the transgranular and intergranular fracture, and the dimples in matrix are elongated along the direction of stress.