An experimental investigation was carried out on the ultra-fine grinding of inorganic powders using a stirred ball mill. The power consumed in the grinding process was measured, and the comminution coefficient, K, in the grinding kinetics equation was examined, based on an analysis of the relationship between the experimental specific surface area and the particle-size distribution of ground products. The effect of grinding aids on the comminution coefficient, K, was also investigated. It was demonstrated that the grinding rate for calcite could be improved by the addition of grinding aids. When using grinding aids, K improved by 16.0% and 34.2% for 60 wt% and 70 wt% slurry concentrations, respectively. Thus grinding aids are very effective in the submicron range grinding process. (C) 2009 The Society of Powder Technology Japan. Published by Elsevier BV and The Society of Powder Technology Japan. All rights reserved.