A series of spinel Li-Mn-Ni composite oxides with theoretical chemical formula of LiNixMn2-xO4 (0≤x≤1.0) were synthesized by liquid phase method. Their structure and morphology were characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM),respectively. The stability of these Ni-substituted spinel oxides prepared at different temperatures was investigated in acidic medium as well. The results show that Ni can be brought into the spinel framework completely to form well-crystallized product when x≤0.5 and the optimized synthesis temperature is 800 °C. LiNi0.4Mn1.6O4 prepared at 800 °C can maintain the spinel structure and morphology with Li extraction ratio of 30.37%,Mn extraction ratio of 8.78% and Ni extraction ratio of 1.82% during acid treatment. The incorporated Ni not only inhibits the dissolution of Mn,but also reduces the extraction of Li due to the lattice contraction. A series of spinel Li-Mn-Ni composite oxides with theoretical chemical formula of LiNixMn2-xO4 (0≤x≤1.0) were synthesized by liquid phase method. Their structure and morphology were characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM), respectively. The stability of these Ni-substituted spinel oxides prepared at different temperatures was investigated in an acidic medium as well. The results show that Ni can be brought into the spinel framework completely to form well-crystallized product when x ≦ 0.5 and the optimized synthesis temperature is 800 ° C. LiNi0.4Mn1.6O4 prepared at 800 ° C can maintain the spinel structure and morphology with Li extraction ratio of 30.37%, Mn extraction ratio of 8.78% and Ni extraction ratio of 1.82% during acid treatment. The incorporated Ni not only inhibits the dissolution of Mn, but also reduces the extraction of Li due to the lattice contraction.