A processing route to disperse carbon black (CB) nanoparticles in aqueous and various organic solvents was developed by a high-shear-agitated bead milling process in water with various cationic dispersant and further surface modification using anionic surfactant. First, for dispersing CB nanoparticles in an aqueous suspension, polyethyleneimine (PEI) and a new cationic dispersant, which was synthesized by the reaction of PEI with a hydrophobic toluoyl group (T-PEI), were used to stabilize CB nanoparticles in water during the bead milling process, and their results were compared. When PEI was used as a dispersant, the conditions for obtaining CB nanoparticles in water in a dispersed state were few and most additive conditions resulted in a segregated and inhomogeneous CB suspension. However, when T-PEI was used as a dispersant, a highly dispersed CB suspension was obtained under a wide range of T-PEI additive conditions, even when the additive amount was as low as 1.0 mg/m2. Next, for dispersing CB nanoparticles in various organic solvents, an anionic surfactant that branched into hydrophilic polyethylene glycol (PEG) and hydrophobic alkyl segments was adsorbed on CB nanoparticles stabilized with PEI or T-PEI. It was found that CB dispersible in various solvents could be obtained successfully only when the anionic surfactant was adsorbed on PEI-stabilized CB nanoparticles. The proposed action mechanism of each surfactant on the CB surface and its effect on the stability of CB in an aqueous/organic solvent are discussed. (C) 2012 Elsevier B. V. All rights reserved.