Mathematical models for ball mills and hydrocyclones were developed using plant data in the grinding circuit of Cayeli Bakir Isletmeleri (Cst) flotation plant. Three sampling surveys were carried out in the circuit. Size distribution and solids content of the samples were determined, and then mass balancing studies were performed. Using the balanced data, the model parameters for ball mills and hydocyclones were calculated. The fit between measured and predicted values was found to be very good both in terms of size distributions and flow rates. Then, different circuit configurations and effects of various operating parameters were evaluated by simulation studies.