Here we report a simple, low-cost and high yield strategy for porous carbon nanosheets (PCNS) with a high specific surface area using corncob waste material as carbon source. The PCNS are used as the conducting matrix for sulfur to form sulfur/porous carbon nanosheets (S/PCNS) composites, which are applied as cathodes for lithium–sulfur (Li–S) batteries. The S/PCNS composites exhibit a high initial discharge capacity of about 1600mAhg−1 and maintain a reversible capacity of 554mAhg−1 after 50 cycles. The superior performance is attributed to the highly porous structure of two-dimensional carbon nanosheets that not only enables stable and continue pathway for rapid electron and ion transportation, but also restrain soluble polysulfides and suppress the “shuttle effect”. The large surface area and unique sheet-like two-dimensional structure of PCNS also leads to a high utilization of sulfur, indicating a promising cathode material for Li–S batteries.