Lithium-sulfur (Li–S) batteries are one of the promising energy storage systems. However, rapid capacity attenuation caused by shuttle effect of soluble polysulfides is a major challenge in practical application. The separator modification is one complementary countermeasure besides the construction of sulfur host materials in cathode. MXene is one type of outstanding candidates for promoting redox kinetics of sulfur species. Herein, recent advances of MXene-based materials as separator modifiers are summarized. The importance of high conductivity and catalytic effects in promoting catalytic conversion of polysulfides and suppressing shuttle effect of polysulfides has been highlighted, and the superiority of MXene for improving reversible capacity and cycling stability has been demonstrated. New strategies for the design of MXene-based separator modifiers are proposed to improve energy density and lifetime. The review provides new perspectives for future development of high-performance Li–S batteries.