Modified lithium manganese oxides were prepared by solid-state reaction of LiMn2O4 and LiCoO2 as raw materials. A study was carried out by TG-DSC,XRD, DSC and electrochemical to analyse the reaction process and structural characterization of products. The results show that the LiMn2O4 reacts chemically with LiCoO2 at high temperature. All of Li and partial Co atoms can insert into the LiMn2O4 crystal lattice and a newly formed spinel phase-modified LiMn2O4 was obtained. The distribution of Co content is even in modified LiMN2O4 compound. The modified LiMn2O4 compound exhibits improved cycling stability at room and elevated temperature in comparison with the pure LiMn2O4.