The effects of ball filling on the selection (S-i) and breakage functions (B-i,B-j) for the natural amorphous silica were investigated in this paper. At four levels (20%, 30%, 40% and 50%) of ball filling, the selection functions and breakage functions were determined by one-size-fraction tests. The selection function was found be quite effective with increasing ball filling for smaller particle size, but it was found to show differently for larger particle size. The breakage functions obtained by direct measurement were studied. When the ball filling was high, the breakage function was appeared to be higher for the natural amorphous silica. The results of tests, the effect of ball filling on the breakage parameters were found to be different than previous studies regarding some results. Therefore, it has appeared that the grinding kinetics for each material must be evaluated in order to lower the energy costs in grinding process. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.