The Fe-Mn based Li-rich materials, Li1+x (Fe y Mn1−y )1−x O2, are highly expected to be potential cathode materials for lithium ion batteries due to high capacity, good safety, environmental friendliness, and low cost. A simple synthesis route, the modified Pechini method, was employed to synthesize the nanosized Fe-Mn based Li-rich materials with excellent electrochemical performance. The structure, particles morphology, and dispersibility of the obtained materials are examined by X-ray diffraction (XRD), scanning electron microscope (SEM)and transmission electron microscope (TEM). The crystallinity and surface area of materials strongly depend on the calcination temperature. The samples calcined at low temperature with small particle size show high discharge capacity, but fast capacity fading due to the poor crystallinity. In order to solve this contradiction, the sample Li1.26Fe0.22Mn0.52O2 was calcined at low temperature (500°C), then heated at high temperature for a short time. It possesses both small particle size and good crystallinity, exhibiting high discharge capacity of about 200mAhg−1 and improved cycleability. The rate performance is excellent that the discharge capacity is about 140mAhg−1 (1C) and 110mAhg−1 (2C), respectively.