Grinding, particularly at finer sizes to achieve the required degree of liberation or specific surface, is a critical unit operation in terms of energy consumption and process optimization. Nowadays, considering the significant developments made in computer hardware and software, using simulation programs to optimize design and operation of various ore treatment plants could be very beneficial to the mineral process engineers. Currently, there are a number of steady-state simulators that can be run under DOS(TM) or WINDOWS(TM) environments such as BMCS, MODSIM(TM) and JKSimMet(TM). In this paper, COMSIM, a new simulator which runs under Excel spreadsheet will be introduced which uses a Population Balance Model (PBM) to simulate ball mills. Plitt and Nageswararao models have been used to describe the performance of hydrocyclones, which by linking to the ball mill model allow for closed-circuit simulations. To describe material flow through the ball mills, two tanks-in-series models called Weller's model and one plug flow unit plus n perfect mixers units (1PF+nPM) model have been used. Utilizing Microsoft(TM) Excel(TM) capabilities such as graphics and VBA programming to implement new macro-based user functions, the authors developed an easy-to-use comminution simulation environment. By comparing the outputs of COMSIM with measured grinding data and previously existing simulators, particularly BMCS, its performance was firmly tested both in terms of accuracy and precision of obtained results. (C) 2006 Elsevier Ltd. All rights reserved.