Simulation of the ultra-fine grinding process is a formidable task, attended to by many researchers using models from conventional ball mill grinding. It has been realised that the first-order breakage hypothesis is not valid in fine grinding and that the process mechanism differs substantially from that for ball mills. In this paper, the difference between ball mill grinding and stirred ball milling is discussed. A size-energy model is proposed for simulation of stirred ball milling. The product size distributions below 10 mu m from a stirred ball mill were simulated by the model satisfactorily. The model is simple and has only two parameters. The model was tested under different milling conditions for a stirred ball mill.