Modifying the surface of MgMn₂O₄ by reduced graphene oxide (rGO) improved the electrical conductivity of the MgMn₂O₄/rGO composite more than that of the pristine MgMn₂O₄. In this study, the performance of the pristine MgMn₂O₄ and the MgMn₂O₄/rGO composite, as cathode materials, was investigated in magnesium-ion batteries (MIBs). Structural studies were performed by using various techniques. The morphology of the MgMn₂O₄ hollow spheres in the rGO substrate was confirmed by the results of FE-SEM and TEM. Raman spectroscopy and X-ray powder diffraction (XRD) also confirmed the successful synthesis and the desired structure. In addition, the electrochemical performance of the cathode active substance was investigated by utilizing different electrochemical methods. The initial capacity of MgMn₂O₄ was approximately 120 mAh g⁻¹, which reduced to 92 mAh g⁻¹ following 100 cycles with the capacity loss of approximately 25%. In comparison, the initial capacity of the MgMn₂O₄/rGO composite was 305 mAh g⁻¹, which decreased to 290 mAh g⁻¹. Based on our results, incorporating rGO improved the performance of the active ingredient.