Li-rich layer-structure xLi2MnO3·(1 − x)LiNi1/3Co1/3Mn1/3O2 (x = 0.2, 0.4, 0.6, 0.8) cathode materials have been synthesized by co-precipitation and microwave hydrothermal (MH) method in a short time (∼60 min). The crystal structure is characterized by X-ray diffraction (XRD) patterns, and refined by two sets of diffraction data (R-3m and C2/m). The morphology is characterized by scanning and high-resolution transmission electron microscope (SEM and HRTEM) which shows the average particle size (50–100 nm). The charge/discharge results indicate xLi2MnO3·(1 − x)LiNi1/3Co1/3Mn1/3O2 (x = 0.4) synthesized at 180 °C for 60 min has the best discharge capacity and cyclic performance. Within the cut-off voltage between 2.5 and 4.8 V, the initial discharge capacity is 325 mA h g−1 at 0.1 C rate; and after 50 cycles the discharge capacity remains 234.5 mA h g−1. The xLi2MnO3·(1 − x)LiNi1/3Co1/3Mn1/3O2 prepared by facile and rapid microwave-assisted hydrothermal (MH) is a promising preparation method in cathode material for lithium ion batteries.