Rapid pyrolysis of several-types of solid carbonaceous materials [lignite, bituminous, coal, and petroleum coke (petcoke)] was conducted in a drop-tube furnace at 1300 degrees C under atmospheric pressure. Soot properties, including yield, particle size, microstructure, and reactivity, were studied, with focus, on the key factors that influence soot gasification reactivity. Results show that the soot yield of bituminous coal is up to 15-20 wt %, which is nearly half of the volatile matter, while those of lignite and petcokes are merely several, percentages of the raw material. The reactivity of soot is lower than that of coal char and higher than that of petcoke char. Among several soots, lignite soot is most active, while petcoke soot displays the lowest reactivity. The catalytic effect of the mineral content is excluded because no alkali metal and alkaline earth metal were detected in soot-sample. The reactivity difference is independent of the particle size but closely related to the microstructure. The soot particles consist of primary spherical or nearly spherical nanometer particles with a recognizable central nucleus of about 5-15 nm. Concentrically arranged graphene layers-form an onion-like structure. Soot formed from lignite has-more-bent graphene layers and a higher amorphous carbon content as a result of lattice defects, coincident with its high gasification reactivity.