A two-stage ball milling circuit for the grinding of molybdenum ore was investigated based upon the grinding kinetic model. To this end, batch grinding tests at the laboratory-scale were conducted to obtain the specific rate of breakage and the primary breakage distribution in wet and dry environments. The test results were then scaled-up to the conditions of a full-scale ball milling circuit for grinding molybdenum ores. A two-stage ball milling circuit algebra was employed to predict the capacity, circulation ratio, and size distributions. Comparison of the simulated results and the observed values showed that the model represents accurately the actual milling process in the plant. Simulation results indicated that the classification in the milling process was operated under non-optimal conditions, and that an increase in the mill output of more than 47% was possible simply by modifying the cut size of the classifier. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B. V. and The Society of Powder Technology Japan. All rights reserved.