The process of interaction of graphene with iron oxide nanoparticles was investigated. First, graphene oxide (GO) modified with magnetite Fe3O4 nanoparticles was successfully synthesized. Raman and MOssbauer spectroscopy revealed that the magnetite Fe3O4 in combination with GO became non-stoichiometric, and the maghemite phase gamma-Fe2O3 appears. Subsequent reduction of graphene oxide by thermal treatment leads to an increase in the fraction of maghemite content and, in addition, the hematite phase alpha-Fe2O3 appears in the sample annealed at above 500 degrees C. Meanwhile, the core-shell nanocomposites of FexOy/G appear, were FexOy consists of a mixture of the Fe3O4, gamma-Fe2O3 and alpha-Fe2O3 phases. The content of each phase can be varied by the annealing temperature. Magnetic, Mossbauer and Raman spectroscopy measurements indicate that graphene can interact with iron oxide. Charge-transfer from iron to graphene can occur due to delocalization of 3d electrons, which reduces the overall magnetic moment of the charge -transfer complexes. These properties can have potential applications in electronic such as supercapacitors, advanced anode materials for lithium-ion batteries, magnetically targeted drug delivery, photothermic therapy, and magnetic resonance imaging.