A monolayer poly(vinyl alcohol) (PVA)-based separator with pendant sulfonate/carboxylate groups and compact morphology is synthesized to suppress the essential lithium polysulfide permeation in lithium sulfur batteries (LSBs). The Li+ transference number is significantly increased to 0.8, much higher than that of a commercial separator (0.43). The polysulfide retention is verified by idle test in a polysulfide-rich electrolyte under the internal electric field of the cell. The LSB with an additive-free electrolyte attains a Coulombic efficiency around 98% and delivered capacity of 804 mA h g-1 at 2.5 A g-1. After 500 cycles, it retains 901 mA h g-1 at 1.5 A g-1 with extra low fading rate of 0.016% per cycle. Overall, this monolayer PVA-based separator provides a facile and effective technique to assemble highly stable LSBs.