The Li-rich cathode materials Li[CoxLi(1/3－x/3)Mn(2/3－2x/3)]O2 with different Co contents (x＝0.4, 0.5, 0.6) were synthesized by modified Pechini method. The results of XRD confirmed that the crystals of the Li-rich compounds possess layered structure and have good crystallinity. The initial discharge capacities of the compounds are high between 200～220 mAh/g, increasing with the increase of Co contents. The material with x＝0.4 exhibits the best cycling property. The capacity retainment is about 75% after 50 cycles at 0.5 C (100 mA/g). The peak of Mn4＋/Mn3＋occurred below 3.5 V in the plots of dQ/dV, and the area of the peak increases with the cycle numbers. The results of the XRD during the cycling process show the layer structure of the Li-rich materials transfers to the spinel phase, and the impurities appears during the cycling, resulting in the capacity fade.