 In this study, cetyltrimethylammonium bromide (CTAB)-modified separator is developed by using a simple and facile method for lithium–sulfur (Li–S) batteries. CTAB is coated on only one side of separator using a doctor blade. The coated CTAB on the separator improves wettability between separator and electrolyte and ionic conductivity of separator. In addition, CTAB also inhibits the migration of dissolved polysulfides to the anode side. These phenomena improve the electrochemical properties of Li–S batteries using CTAB-coated separators. Cells using the CTAB-coated separator exhibit an initial capacity of 1136 mAh g−1 at 0.2 C-rate. In addition, they can maintain a higher capacity (765 mAh g−1) and capacity retention rate (67.3%) after 150 cycles as compared to pristine Li–S batteries (549 mAh g−1 and 48.5%, respectively). These results indicate that the CTAB-coated separator can enhance the performance of Li–S batteries.