The effect of the shape of grinding media on the breakage parameters of colemanite has been investigated in kinetic studies. In this present research, three different monosize fractions, i.e., -425 + 300 mu m, -300 + 212 pm and -2.1.2 + 150 pm, were used. The grinding media used for the tests were 36.5 x 36.5, 30.1. x 30.1, 25.4 x 25.4, 19.05 x 19.05 and 12.7 x 12.7 mm diameter cylinders, and 36.5, 30.1, 25.4, 19.05 and 12.7 mm diameter balls made from cast iron. The specific rate of breakage (Si) and model parameters (a(T), alpha) were evaluated for the same quantity of cylinders, balls and feed material. The values of S(i) and the model parameters indicated that a faster breakage rate can be obtained by using cylinders as the grinding media. The size distributions of the products showed that the use of cylinders for grinding offers advantages for relatively coarse feeds. At shorter grinding periods, the product fineness from cylinder grinding was greater than that from ball grinding. However, after progressive grinding, the product fineness of ball grinding eventually exceeded that of cylinder grinding. The overall results indicated that the shape of the grinding media plays a determining role in the overall process.