The distribution, morphology, composition as well as the transition of metastable carbides MC' in the initial atomized powders and in the various subsequent treatments in Ni-base P/M superalloy FGH95 have been studied. MC' has many kinds of complex morphologies and contains a large number of non-carbide forming elements. Conversion of MC' to stable MC during HIP consolidation promotes the formation of PPB carbides.Stabilization treatment applied to loose powders can improve the stability of MC' and change its distribution. HIP consolidation and hot extrusion can effectively eliminate PPB carbides and be expected to improve the alloy property.