Sulfur-free and sulfur-containing carbon phases have been synthesized from methane using a carbonyl iron catalyst and modified by melting with sulfur. The particle size distribution measurements show that the particle radii are shifted to smaller values after the reaction with sulfur. The content of sulfur in the modified carbon fractions depends on the particle size. In AFM images of some fractions, thin platelets of graphite (thickness of ca. 10 nm) have been seen. XRD analysis points on the aggregation of the carbon particles, which occurs at once with the sedimentational fractionation. Taking into account a tendency to increase the sulfur content inverse proportional to the particle size in the fractions, one can suggest that the sulfur is more likely to react with the finest ingredients of synthesized carbon phase. (C) 2006 Elsevier Ltd. All rights reserved.