In this study, the effect of powder filling was investigated on a pumice sample from the Karakaya region of Isparta in Turkey using dry batch grinding conditions and a kinetic model. Eight different mono-size fractions, between 1.7 and 0.106 mm, were prepared using a root2 sieve series. The specific rates of breakage (S) and the primary breakage distribution (B-ij) equations were determined from the size distributions at different grinding times, and the model parameters were compared for the five different powder filling levels. In many investigations, it has been found that an interstitial filling fraction of U = 0.6 to 1.1 is a good powder-ball loading ratio to give an efficient breakage in a ball mill. In this research, it was found that U = 0.4 is a good ratio for the pumice sample. (C) 2002 Elsevier Science B.V. All tights reserved.