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Mn-doped spinel oxides Mn_xNi_1−xCo₂O₄ (x = 0, 0.3, 0.5, 0.7, and 1) were synthesized using the citric acid-assisted sol–gel method. The Mn_0.5Ni_0.5Co₂O₄ (x = 0.5) supported on carbon nanosheets, Mn_0.5Ni_0.5Co₂O₄/C, was also prepared using the same method employing NaCl and glucose as a template and carbon source, respectively, followed by pyrolysis under an inert atmosphere. The electrocatalytic oxygen reduction reaction (ORR) activity was performed in alkaline media. Cyclic voltammetry (CV) was used to investigate the oxygen reduction performance of Mn_xNi_1−xCo₂O₄ (x = 0, 0.3, 0.5, 0.7, and 1), and Mn_0.5Ni_0.5Co₂O₄ was found to be the best-performing electrocatalyst. Upon supporting the Mn_0.5Ni_0.5Co₂O₄ on a carbon sheet, the electrocatalytic activity was significantly enhanced owing to its large surface area and the improved charge transfer brought about by the carbon support. Rotating disk electrode studies show that the ORR electrocatalytic activity of Mn_0.5Ni_0.5Co₂O₄/C proceeds via a four-electron pathway. Mn_0.5Ni_0.5Co₂O₄/C was found to possess E_1/2(V) = 0.856, a current density of 5.54 mA cm⁻², and a current loss of approximately 0.11% after 405 voltammetric scan cycles. This study suggests that the interesting electrocatalytic performance of multimetallic transition metal oxides can be further enhanced by supporting them on conductive carbon materials, which improve charge transfer and provide a more active surface area.