Sulfur–carbon nano-composites were prepared by two methods: thermal treatment and mechanical milling. The resulted composites were characterized by scanning electron microscopy, X-ray diffraction and Brunauer–Emmett–Teller. The structures and electrochemical properties of the composites were decided by the preparation methods and sulfur contents. By thermal treatment, most part of sulfur could be embedded in the micro pores of the active carbon. Combined with polymer electrolyte, the composites with favorable sulfur contents exhibited high specific capacity up to 800 mA h g−1 in the initial cycle and a stable reversible capacity approximately 440 mA h g−1. The utilization of electrochemically active sulfur was about 90% assuming a complete reaction to the product of Li2S.