In this study we have investigated new magnetic nanocomposites (MNCs) graphene oxide (GrO)/magnetite (Fe3O4) + cobalt ferrite (CoFe2O4) of various concentrations that were synthesized by the mechanochemical method—the process of mechanical grinding in a ball mill in the aqueous medium of graphene oxide and preliminarily synthesized powders of magnetite and cobalt ferrite. We have obtained and studied MNCs GrO/Fe3O4 + CoFe2O4 obtained by grinding with various contents of components (in wt %), namely: 50/40 + 10; 50/25 + 25; 50/10 + 40; and 50/0 + 50. The synthesized MNCs GrO/Fe3O4 + CoFe2O4 have been investigated by X-ray diffraction method, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, a vibrating sample magnetometer, and Mössbauer spectroscopy. With the help of Mössbauer investigations, the phase composition, magnetic state, and structure of synthesized MNCs GrO/Fe3O4 + CoFe2O4 have been established, which is important for creating high-performance materials for various applications. The heterogeneity of the MNCs obtained opens prospects for their biomedical applications.