Expanded graphite/sulfur (EG/S) composites were prepared by microwave irradiation of mixtures of sulfur and expanded graphite with S/EG ratios from 4:1 to 12:1. Sulfur was sublimed and entered the EG pores when the mixtures were heated and was condensed to form particles within the pores during cooling. The pores of the EG acted as microcontainers to host the sulfur, and the material, with its interconnected and conductive pore walls, acted as a current collector for the cathode of the Li-S battery. The size of sulfur particles in the EG pores could be controlled by the S/EG mass ratio. When the ratio is 10:1, relatively uniform size sulfur particles could be obtained. Both the S/EG ratio and the sulfur particle size have an important effect on the capacity increase of the Li-S battery. Using a composite with a S/EG ratio of 10:1 as the cathode gives the highest capacity of 1 020 mAhg⁻¹ at a rate of 0.1 C.