An investigation on the kinetics of grinding quartz was carried out in a laboratory stirred ball mill. In this study, the specific rate of breakage S and breakage function B were determined by one-size-fraction tests. The results showed that below a certain size, the breakage was first-order and the breakage functions were normalizable. Compared with the breakage of same material in a tumbling mill, the S values in a stirred mill were more than a magnitude higher. Nevertheless, in contrast with the case in a tumbling mill, the simulation of size distribution by using these experimental S and B values gave no agreement with the observed data. The study showed that due to the environment effects by a high force action in this kind of mill, the breakage rate for small sizes was affected by large sizes, differing from the breakage of one size fraction. Considering this effect, a reasonable expression of S was given and gave a better simulation of grinding.