Ni-based superalloys belong to the group of materials that are difficult to machining, hence, precision casting is almost irreplaceable in aircraft blades manufacturing. One of the last stages of the production cycle is heat treatment, which allows the shaping of the final microstructure and mechanical properties of castings. As part of this work, an analysis of the influence of heat treatment on the microstructure changes of the DS MAR-M247 Ni-based superalloy was performed. Observations and analyses of castings were carried out using: thermodynamic simulations, differential scanning calorimetry (DSC), X-ray diffraction (XRD), light microscopy (LM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), scanning-transmission electron microscopy (STEM). It was shown that heat treatment led to partial dissolution of the precipitates of the γ' phase and complete dissolution of the M5B3 borides and the Ni7(Hf, Zr)2phase. Secondary γ' precipitates in dendritic areas are characterized by cubic morphology and smaller size than before heat treatment. In the interdendritic spaces, the secondary γ' precipitates have a much more complex morphology, which is related, among others, to the coagulation of smaller precipitates during heat treatment.