In this study, the flow properties of black soybean powders having different particle sizes (d(90) = 1448.66, 1484.14, 1458.18, 1385.73, 1246.89, 740.06 mu m) were measured, and the flow characteristics were applied to a hopper design. For a given black soybean powder, reducing the particle size tends to reduce flowability. At the smallest particle size (d(90) = 740.06 mu m), the flow function was located in the cohesive region and the ratio of change in the bulk density increased from 4.72% to 19.13% as the particle size decreased from d(90) = 1448.66 mu m to 740.06 mu m. The results of the internal friction angle at different particle sizes were not exactly consistent with the results of the flow function, which could be a result of the different particle shapes in addition to the different sizes. Image processing of particles with different particle sizes revealed a difference of HSC (high sensitivity circularity), and particles with more circular shapes showed a lower internal friction angle. The black soybean powders with the smallest particle size showed poor flowability and required larger values of the hopper angle and a larger minimum size of the hopper opening. (C) 2014 Elsevier Ltd. All rights reserved.