To develop a method for measuring the flowability of MOX (mixed oxide of uranium and plutonium) particles used in the simplified MOX pellet fabrication process, the flowability of model particles has been investigated by the vibrating tube method. As model particles, pulverized ZrO2 and granulated WO3 were used. To prepare a variety of samples, coarse particles of 106-250 mu m in diameter were mixed with fine particles smaller than 45 mu m in diameter in different concentrations. The prepared particles were put into the vibrating tube and the amplitude of vibration was increased at a constant rate for a period of time and then decreased. The mass of particles discharged from the tube was measured at constant time intervals. From the experimental data, the relationships between the mass flow rate and the vibration acceleration (i.e. flowability profiles) were obtained. Two factors (i.e. 'critical vibration acceleration' to make the particles flow and 'characteristic mass flow rate') were selected to analyze the flowability profiles. The hysteresis of the flowability between increasing and decreasing vibration accelerations was also evaluated. (c) 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.