Corn. C black was treated with radio-frequency plasma (13.56 MHz) in Ar or 1,3-butadiene flow in a rotary lab. plasma reactor to activate its surface. The product was studied for surface grafting and oxidn., sp. surface area and surface energy and then used as filler for natural rubber. The highest degree of C black modification was reached after the butadiene plasma activation for 5 min followed by the monomer flowing through the reactor for another 3 min, in order to sat. active centers on its surface. After vulcanization, the rubber was studied for surface morphol. and mech. properties. The plasma-assisted modification of C black resulted in an improvement of interphase interactions and the degree of filler dispersion and distribution in the rubber matrix. No improvement of mech. properties of the rubber vulcanizates was, however, obsd.