This work demonstrates the effect of atomic layer deposited (ALD) Al2O3 on the reactivation of dissolved polysulfides in Li–S batteries. A 0.5nm thick layer of Al2O3 is conformally coated onto highly porous carbon cloth by ALD, and then assembled in a Li–S battery between the sulfur cathode and the anode side (separator and Li anode) to function as a reactivation component. Compared to half cells with no ALD treatment, the ultrathin Al2O3 coating increases the specific discharge capacity by 25% from 907 to 1136mAh/g at the 1st cycle, and by 114% from 358 to 766mAh/g at the 40th cycle. Thus the ALD-Al2O3 improves the initial specific capacity and stabilizes the cycle life remarkably. Scanning electron microscopy and energy-dispersive X-ray spectroscopy results indicate that the ALD-Al2O3 coated carbon cloth sorbs (adsorbs/absorbs) more dissolved sulfur species from the electrolyte. Potential mechanisms for the improved sorption properties are proposed. The combination of an ultrathin ALD-oxide coating with highly porous carbons presents a new strategy to improve the performance of Li–S batteries.