The particle size distribution of the solids forming a slurry has a predominant role because of its direct effect on the slurry's rheology. The process of comminution, which is the most important factor affecting the cost of the slurry preparation, is directly affected by the particle size distribution. Control or particle size and size distribution is generally considered to be the means for reducing slurry viscosity in the field of coal-slurry research. it is believed that by controlling particle size distribution and particle loading coupled with the use of additive chemicals, a coal-water slurry can be economically produced that is compatible with the physical characteristics needed for storage, handling, and burner nozzle atomization. In this study the effect of particle size distribution on the rheology of lignite-water slurries was investigated, and the optimum particle size distribution was obtained for the lignite particle size less than 125 mu m. The relation between the apparent viscosity of the slurry at the shear rare of 100 s(-1) and the particle size distribution was demonstrated. Sedimentation behavior of the slurries prepared was also investigated.