Talc particulates were ground by a high-speed rotor mixer without grinding media (beads) under atmospheric condition in order to evaluate the performance of the mixer. The median diameter of the ground sample decreases with an increase in both rotational speeds of the rotor and the vessel, and with a decrease in the clearance in the working space. The grinding limit can be controlled by the operational conditions. The grinding limit is correlated with the tangential force acting on the particulates calculated from the particulates motion simulated by the Particle Element Method regardless of the rotational speeds and the clearance.