A method for preparing a sulfur-carbon composite including the steps of: (a) mixing a carbon-based material with sulfur or a sulfur compound; (b) placing the sulfur-carbon mixture mixed in step (a) and a liquid which is vaporizable into a sealable container; and (c) heating the sealed container to a temperature of 120 to 200° C.; a positive electrode for a lithium secondary battery including the sulfur-carbon composite prepared by the above method, and a lithium secondary battery including the above positive electrode.