Abstract: The inflnence of Iron (0-25%) on the microstructure and properties of a cast Nickel-Base superalloy is examined The results of this study show, that the gamma prime fraction in alloy and gamma prime size decrease with the Iron addition in alloy. The morphology of gamma prime is changed from cube to spheroid and the amount of MC is increased, but both amount of M₂₃C₈ and M₃B₂ are reduced as Iron coutent iucreases. The partition ratio of alloying elements between γ-γ' is changed and average electron-vacancy number $\bar N$v is increased apparently by Iron addition in alloy, thus the precipitation of sigma phase is accelerated. The amount of harmful elements is increased with Iron addision in alloy. Iron addition in alloy severely decreases the stress repture, but slightly iufluences the tensile strength of this cast nickelbase superalloy. Simultaneously, the ductility of alloy with high Iron content is low.