Paint, magnetic paint, printing ink and highly concentrated slurry belong to the suspension where solid particles disperse in liquids. Rheological properties of the slurry are important in an industrial operation. Especially, it is valuable to lower the viscosity of slurry, so as to reduce the pressure drop in a slurry transport. In this paper, the apparent viscosity of highly concentrated slurry is measured and the effect of additives on theapparent viscosity is investigated using TiOo2 (rutile type), Fe203 (a type) and A1203 as dispersion particles and water as dispersion medium, respectively. The used additives are sodium hexametaphosphate, sodium oleate and polyacrylic acid. The obtained results are summurized as follows. The van der Waals\u27 attractive force and electro-static repulsive force are significantly concerned with the apparent viscosity of slurry. Sodium hexametaphosphatehas an excellent effect that it remarkably reduces the apparent viscosity of Ti02 and Fe203 slurries. Sodium oleate behaves to reduce the apparent viscosity of Fe203 slurry due to the chemisorption on the Fe203surface
