Co0.5Mn0.5La x Fe2−x O4 precursor was synthesized by solid-state reaction at low temperatures using CoSO4 ⋅7H2O, MnSO4 ⋅H2O, FeSO4 ⋅7H2O, La(NO 3)3 ⋅6H2O, and Na2 CO 3 ⋅10H2O as raw materials. Co0.5Mn0.5La x Fe2−x O4 was obtained by calcining carbonates precursor in air. The precursor and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, X-ray powder diffraction, scanning electron microscopy, and vibrating sample magnetometer. A high-crystallized Co0.5Mn0.5La x Fe 2−x O4 with a cubic structure was obtained when the precursor was calcined at 700 °C in air for 2 h. The specific saturation magnetizations and coercivity of Co0.5Mn0.5La x Fe2−x O4 depend on the calcination temperature and composition. The thermal transformation of Co0.5Mn0.5CO3–Fe2O3⋅0.967H2O from 700 °C in air presented two steps. The values of the activation energies associated with the thermal transformation of Mn0.5Co0.5CO3–Fe2O3⋅0.967H2O were determined based on the Kissinger–Akahira–Sunose (KAS) equation