A multi-scale study of the microstructure of various size spherical powder particles of the rapidly quenched powders of the two Ni-based superalloys produced by PREP-technique for using in PM HIP technology was performed. Methods of metallography autoradiography on carbon and boron SEM EDX EBSD were used to study the microstructure and distribution of alloying elements with low and high magnification. The composition of matrix segregations of the alloying elements and precipitates of the carbides and borides phases was determined. Effects of the spherical particles size on the regularities of the microstructure formation were revealed. Growth of dendrites with slightly larger dendrite arm spacing was observed in bigger spherical powder particles preferably from the surface. Whereas in smaller particles was observed formation of the cellular structure on surface and dendrite crystals in the bulk of particles. Effect of superalloy composition on the features of dendrites structure and precipitates composition was defined.