Abstract: The effect of structural defects on the formation of quench cracks in a Nickel-base P/M superalloy was studied. The serious quench crack is due to the presence of rich-oxygen layer on the.Particle surface and the formation of PPB carbides destroying the continuity of the alloy and promoting fracture along the previous particle boundaries. The slight quench crack is due to the precipitation in a coarse form at the grain boundaries. The coarseγ' precipitates are surrounded by zones depleted Al,Ti froming oxide layers which promote the fracture path along the grain boundaries. The major reason of the formation of quench cracks is the contamination of oxygen in the early processing or unsuitable quench cooling rate during heat treatment.