PURPOSE: To produce grafted carbon black having excellent compatibility to plastics and elastomers, by applying ionizing radiation to a system obtained by contacting carbon black with a vinyl monomer.

CONSTITUTION: Carbon black such as acetylene black, furnace black, thermal black, etc. and one or more vinyl monomers (e.g. styrene, vinyl chloride, isoprene, etc.) are put into, e.g. a polymerization tube, and polymerized at 20W80°C under irradiation with ionizing radiation, preferably under rotation or oscillation of the tube tobtain the objective grafted carbon black. The contact of the vinyl monomer with carbon black is preferably carried out in vapor phase.