In this study, optimization of some parameters of stirred mill on ultra-fine grinding of refractory Au/Ag ores was performed. A three-level Box-Behnken design combining a response surface methodology (RSM) with quadratic programming (QP) was employed for modelling and optimization of some operating parameters in ultra-fine grinding. Grinding tests were carried out in a laboratory scale pin-type vertical stirred mill. The relationship between the response, i.e. d(80) size, and four grinding parameters, i.e. ball diameter, grinding time, ball charge ratio and stirrer revolution was presented as empirical model equations. Analysis of variance showed a high coefficient of determination value (R-2=0.9698), thus ensuring a satisfactory of the second-order regression model with the experimental data. The model equations were then optimized using the quadratic programming method to minimize for 40 size within the experimental range studied. The optimum conditions were found to be 1.61 mm for ball diameter, 11.50 min for grinding time, 80% for ball charge ratio and 745 rpm for stirrer revolution for this grinding process. In order to verify the improvement of grinding performance using the optimal level of control factors three verification experiments were conducted, and the results for d(80) was 3.37 mu m, which were smaller than those obtained in the initial tests. (C) 2010 Elsevier B.V. All rights reserved.