Our group has proposed a jet mill equipped with a particle-trap ring at the exit of the comminution zone to prevent the escape of large particles entrained by shortcut flow. The visualized swirl flow compares favorably with simulation results obtained by CFD. Experimental results reveal that a trap ring with a height of 4 mm is the most effective for attaining high classification performance. Yet the classification efficiencies measured at various ring heights are much lower than the classification efficiencies calculated by the CFD. This discrepancy may be attributable to the particle-flow interaction and the change in particle size during the particle movement. (C) 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.