The microstructural rejuvenation through non-conventional heat treatments (NCHT) of a conventional cast superalloy Inconel 939 was investigated. The primary and secondary main constituents of the NCHT microstructures were characterized through its morphology and composition applying conventional microscopy and analytical scanning electron microscope (SEM). The results showed a complete rejuvenation of the overage microstructure (disordered coarse cuboids of 1.2μm from γ´, continuous films of M23C6 carbides and coarse MC carbides as well as γ-γ´eutectics) into a more homogeneous microstructure; spherical ordered primary γ´ and secondary γ´ precipitates ranging between 357 to 442 nm and 30 to50 nm respectively and depending on the applied heat treatment. Also blocky type MC and discreet M23C6 carbides dispersed within the dendrite and in the interdendritic regions were observed. There was no evidence of the formation of detrimental phases with the NCHT, which can affect the long-term properties of the alloy during service.