The enhanced electrochemical performance of the lithium-rich solid solution Li1.2[Mn0.54Ni0.13Co0.13]O2 (LMNCO) cathode is enhanced by sulfur incorporation. Various sulfur contents are introduced by adding (NH4)2SO4 into the raw material. The effects of different sulfur contents on the structure, morphology and electrochemical performance are investigated. The original sample (as-received sample) and the sulfur incorporated samples were characterized by X-ray Diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM), Electrochemical Impedance Spectroscopy (EIS), X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy (FTIR). Electrochemical performance such as charge/discharge capacity and rate capability was assessed with lithium ion cells. XRD patterns show that a new phase of Li2SO4 was formed and distributed on the surface of the particle. The electrochemical performance of the sulfur incorporated LMNCO samples is significantly improved due to the formation of the new phase on the surface of the particles. In comparison with the original material, the modified materials show an improved rate performance attributed to the interface between LMNCO and the second phase, which may provide fast diffusion channels for lithium ion.