Dispersion of carbon black powders in aqueous medium was investigated by using anionic surfactant sodium oleate and a series of nonionic surfactants which were selected systematically to represent varying degrees of ethoxylation. Single and binary mixtures of the nonionic and ionic surfactants were employed in zeta potential and particle size measurements and a high affinity of surfactants on carbon black powders was beheld as they significantly changed the zeta potential and size distribution of the powders. But, noticeable differences between the surfactants were also observed, for example, as the nonionic surfactants reduced the absolute magnitude of zeta potential of powders in a wide pH range of 3.0-11.0, Na oleate made the zeta potential of the powders more negative under similar experimental conditions. The carbon black suspensions were agitated in a vessel having a standard geometry and the particle size measurements wet e carried out at desired time intervals without disturbance of the suspensions and interruption of agitation. Effect of surfactants on stability and dispersion of the powders were recognized with the reduction in mean particle sizes, as, in the absence of surfactant, the inean particle size could not be reduced below 24.0 mu m even after 210 min of stirring, it could be reduced to 5.35 mu m after 120 min of stirring in the presence of only 30 g/L of nonionic surfactant. Generally, it Was found that nonionic surfactants could wet and stabilize carbon black powders in aqueous medium better than anionic surfactant. The reason was explained by molecular structure and bulk properties of surfactants. (C) 2009 Elsevier B.V. All rights reserved.