A measuring technique to visualize the motion of media particles has been developed for a horizontal type sand mill, in which internal blade and external cylinder rotate inversely and independently, Using this experimental technique, velocity distribution, intensity of velocity fluctuations and appearance frequency of grinding media in the mill can be measured. Relating to these flow characteristics of media particles for both rotation methods, the grinding performance of calcium carbonate with alumina beads is discussed. As a result, it is found that the median diameter of ground products obtained in both rotation methods can not be correlated only with the intensity of velocity fluctuations having been used to date, but can be correlated well with the intensity of velocity fluctuations weighted by appearance frequency.