We report herein a three-dimensional structured carbon material as the cathode supporter for rechargeable lithium−sulfur batteries. Highly porous activated carbon foam (ACF) with micromesoporosity has been synthesized through carbonizing pomelo peel and activating by KOH. Elemental sulfur has been loaded to the micropores through a solution infiltration method to form a S/ACF nanocomposite. The resulted S/ACF nanocomposite with 60% sulfur has been tested as novel cathodes for Li−S batteries. The S/ACF nanocomposite showed an initial discharge capacity of 1258 mAh g−1 at 0.2C rate. After 100 cycles of charge/discharge, the S/ACF nanocomposite retained a high specific capacity of 750 mAh g−1 with a Coulombic efficiency of 96%. The material delivered a capacity of more than 700 mAh g−1 at 2C rate and can be recovered to 880 mAh g−1 when the rate is returned to 0.2C. The results show that the ACF with 3D connected structure could be a promising binder-free cathode supporter for rechargeable Li−S battery with high specific energy.