Abstract: Water vapor is injected into a gaseous heat carrier passing into a reaction chamber as a plasma stream, contacting a hydrocarbon feed stock there is injected water vapor, and introduced presaturated with water vapor. Under the effect of the heat carrier temperature, the feedstock is decomposed to carbon black which, after being quenched, is collected, for example, by cyclones.The proposed process makes it possible to decrease the degree of polydispersion of the carbon black obtained and also to produce carbon black with a specific geometrical surface within the range of from 50 m.sup.2 /g to 250 m.sup.2 /g, without altering the construction of the reaction chamber.The proposed process avoids the formation of laminated structures, pyrolytic carbon and graphite in the carbon black, which improves the quality of rubber based on these carbon blacks insofar as their abrasive resistance and tensile strength are concerned. Besides, the proces makes it possible to conduct the carbon black-forming reaction within 10.