Humic acid was prepared from Yallourn coal, which is a typical low rank coal. To increase the solubility in water of the prepared humic acid, protons of its carboxyl groups were exchanged for Na (+). The Na+-exchanged humic acid was applied as a dispersing agent for CWM, and its dispersing ability was evaluated by the measurement of CWM viscosity. As a result, the viscosity was found to decrease with addition of the Na+-exchanged humic acid and to be minimized on addition of a certain amount. At this amount, the coal particles in CWM reach adsorption equilibrium of the Na+-exchanged humic acid and a constant negative value of the zeta potential. Next, the prepared humic acid was anodically oxidized in an attempt to improve its dispersing ability. Although no significant improvement was found in the dispersing ability, the oxidized humic acid become more soluble in water and required less NaOH for its solubilization than the unoxidized humic acid.