We investigated the formation of LiMn2O4 phases by calcinating a stoichiometric mixture of Li2CO3 and various manganese compounds with high temperature X-ray diffraction (HT-XRD) technique to understand the influence of starting materials on the electrochemical performance. XRD measurements were carried out during heating processes from room temperature to 700°C. In case of Li2CO3/electrolytic manganese dioxide and Li2CO3/MnCO3 mixtures used as starting materials, Li0.33MnO2 phase and low crystalline phase, respectively, appeared as intermediate products during heating process followed by the crystallization into the spinel. HT-XRD observation confirmed that the LiMn2O4 phase was directly formed from starting Li2CO3/Mn2O3 and Li2CO3/Mn3O4 mixtures. The reactivity of the mixture, meant by the lower reaction temperature between Li and Mn compounds and the faster evolution of Li–Mn–O phase, depended on manganese compounds. The purity and stoichiometry of spinel type LiMn2O4 was not achieved only by the higher reactivity. From these results, the dependence of reversible capacities and cycleability of synthesized LiMn2O4s on the formation process which varied with the starting materials was discussed.