Lithium-sulfur (Li-S) batteries have been attracting growing attention due to the high theoretical energy density (2600 Wh kg−1). Nevertheless, the shuttle effect caused by the diffusion of polysulfides obstructs the further development of Li-S batteries. In this work, graphitic carbon nitride (g-C3N4) with enriched polysulfides adsorption sites of pyridinic-N has been utilized as one kind of chemical adsorption materials to restrict the migration of polysulfides. The vacuum-filtration technique has been employed to cover an ultrathin g-C3N4 film onto the commercial polypropylene (PP) separator (denoted as g-C3N4 separator) which has an effective suppression of polysulfides travel without increasing the mass of the whole battery. Besides, this strategy is simple, straightforward, and effective. As a result, an excellent reversible capacity of 829 mA h g−1 is retained at 0.2C after 200 cycles, much better than that of the battery with a traditional PP separator. Meanwhile, when coupled with the g-C3N4 separator, the Li-S batteries also shows lower self-discharge rate. This result shows a great potential for the mass applications of g-C3N4 separator for Li-S batteries.