The influence of γ-γ′ eutectic on the yield strength and ductility of conventionally cast MAR-M 247 was examined. The amount of the γ-γ′ eutectic present at the interdendritic-grain boundary regions was varied by heat treatment below and above the γ′ solvus temperature. The room temperature yield strength increased and the ductility decreased as the amount of γ-γ′ eutectic was reduced. These results are attributed to the fact that the γ-γ′ eutectic possesses a lower strength and greater ductility than the dendrite cores do. As a consequence, the ductile γ-γ′ eutectic hinderes crack propagation and causes a changes in the fracture morphology as the amount of γ-γ′ eutectic is reduced. © 1988.