Room temperature grinding of talc powder was conducted by a planetary ball mill using media balls of different sizes. The grinding behavior of the talc sample was investigated by X-ray diffraction (XRD) and particle size distribution analyses. The motion of the balls in the mill with talc powder was simulated by the Particle Element Method (PEM) under the same condition as that of the talc grinding. Within the size reduction range of the talc powder, the 50% passing particle size, D-50, of the ground product is expressed by the equation, D-50,D-t/ D-50.0 = (1 - D-50.1/D-50.0)exp( - K(p)t) + D-50.1/D-50.0, when K-P is the rate constant and subscripts, 0, t and 1 denote the initial and arbitrary times, and the grinding limit. The amorphization process of talc powder during milling is expressed by (I/I-o) = exp(K(S)t), where I denotes the representative peak intensity of the XRD pattern of the talc sample ground for arbitrary time, and subscript 0 the initial stage and K-S the rate constant of the amorphization. Both K-P and K-S tend to increase with a decrease in the ball diameter, d, when the mill speed is high. A similar trend can be seen in the relation between the impact energy of balls, E-i, and d. Therefore, both the size reduction and amorphization rates of talc correlate with E-i.