Mechanical activation followed by rotary heating has been successfully applied to the synthesis of Cr-doped lithium manganese oxide (LiMn2O4) powders. The precursor of LiCr x Mn2−x O4 for Li-ion batteries has been synthesized from LiOH·H2O, MnO2, and Cr2O3 as starting materials by mechanical activation, which ensured a high level of homogeneity in the chemical composition of the precursor and resulted in a reduction in the synthesis temperature and heating time. Highly crystallized LiCr x Mn2−x O4 (0.04≤x≤0.10) powders were obtained by subsequent rotary heating of the precursor at 550–750°C for 2h. Rotary heating enhanced the experimental control in chemical composition, particle size distribution and microstructure of the final products. The optimum mechanical activation condition was determined based on XRD analysis. The synthesized LiCr x Mn2−x O4 powder has a narrow particle size distribution, high discharge capacities and good cyclability. The method of mechanical activation combined with rotary heating should be an excellent technique of decreasing synthesis temperature and shortening heating time, and enhancing the uniformity of particle size of the product.