Sulfur is one of the most common vulcanization agents used in the rubber industry to create a three-dimensional network between rubber molecules to improve the physical and even thermal properties of the rubber. Curing agents used in this research are polymeric sulfur (insoluble sulfur, IS) and rhombic sulfur (RS). These two allotropes of sulfur are compared with regard to their ability to vulcanize styrene-butadiene rubber (SBR). Similar results are obtained for both curing agents in term of rheological behavior, and physical and thermal properties. Mooney viscometer and aging tests give higher values for IS-vulcanized SBR, whereas RS-vulcanized SBR shows better cure behavior, hardness, tensile strength, tear and compression set, test results. Despite the similar results, insoluble sulfur does not exhibit blooming and may be able to replace rhombic sulfur as a curing agent in the rubber industry.