The role of aminopropyltriethoxysilane in the interaction between ISAF carbon black and carboxylated nitrile rubber was studied by measurements of bound rubber, physical and dynamic mechanical properties of the vulcanizates, and Monsanto Rheometric studies on the rubber-filler mixes. It is believed that -NH2 groups of the silane interact with - COOH groups of the rubber, while - OC2H5 groups of the silane interact with - OH groups on the filler surface. Weak rubber-filler bonds formed during mixing are converted into a crosslinked structure during high-temperature molding. The extent of crosslinking of the rubber phase by the active sites on the filler surface is greater in the case of oxidized ISAF carbon black, as compared to the nonoxidized grade.