The high-energy lithium/sulfur (Li/S) battery has become a very popular topic of research in recent years due to its high theoretical capacity of 1672 mAh/g. However, the polysulfide shuttle effect remains of great concern with a great number of publications dedicated to its mitigation. In this contribution, a three-dimensional (3D) reduced graphene oxide/activated carbon (RGO/AC) film, synthesized by a simple hydrothermal method and convenient mechanical pressing, is sandwiched between the separator and the sulfur-based cathode, acting as a functional interlayer to capture and trap polysulfide species. Consequently, the Li/S cell with this interlayer shows an impressive initial discharge capacity of 1078 mAh/g and a reversible capacity of 655 mAh/g even after 100 cycles. The RGO/AC interlayer impedes the movement of polysulfide while providing unimpeded channels for lithium ion mass transfer. Therefore, the RGO/AC interlayer with a well-designed structure represents strong potential for high-performance Li/S batteries.