The dispersion stability of nano-sized carbon black produced by a thermal plasma process was investigated using a novel multiple light scattering method. The effect of surface modification of carbon black on the dispersion stability was monitored in various polar and non-polar liquids including water, methanol, styrene, and toluene. The results show that carbon black functionalized with carboxylic anion groups has much improved colloidal stability in a polar solvent and the degree of dispersion stability is strongly related to the solubility parameter value of liquids. In addition, the carbon black with carboxylic anions has a long-term stability without any auxiliary dispersion agent such as a surfactant due to electrostatic repulsion.