IsaMill is a high speed stirred mill for high efficiency grinding of mineral ores and concentrates. A numerical model based on the discrete element method (DEM) was developed to study flow of grinding media in IsaMill. The DEM model was first verified by comparing the simulated results of the flow patter, mixing pattern and power draw from those measured from a 1:1 scale lab mill. Then the flow properties were analysed in terms of flow pattern, flow velocity, force field and power draw. The effects of parameters relating to particle material (i.e., sliding friction coefficient and damping coefficient) and operational conditions (i.e., rotation speed and solid loading) were investigated. While the damping coefficient showed a negligible effect for the range considered, other three parameters had strong effects on the flow properties. Increasing the sliding friction caused the flow velocity and compressive force to have minimum values due to the competitive mechanisms for energy transfer and dissipation, but increased the power draw. The increase in the rotation speed and solid loading also increased the flow velocity, compressive force and power draw of mill. The particle scale, information obtained would be useful to understand the fundamentals governing the flow of grinding media in IsaMill. (c) 2006 Elsevier Ltd. All rights reserved.