We report the synthesis of Mn_xNi_1-xO and Mn_yCo_1-yO alloy nanoparticles by the thermal decomposition of the metal precursor in a surfactant. The different sized and shaped Mn_xNi_1-xO and Mn_yCo_1-yO nanoparticles could be obtained by controlling precursors and surfactants. These alloy nanoparticles are antiferromagnetic and their stability is better than that of pure metal mono-oxides. On the basis of these results, we expect these alloy nanoparticles to have potential applications as electrodes in energy-generating devices such as Li-ion batteries. The higher Ni content (Mn_0.19Ni_0.81O) electrode exhibited a large reversible capacity (650 mAh g^–1), a better initial efficiency (56%), and an improved rate and cycle performance, which was ascribed to higher electrical/electrolyte conductivity or improved surface film property. To our best knowledge, the reversible Li storage in metal oxides like MnO or NiO …​