To improve particle flowability, a technique is used in which fine particles are admixed with the main particles. However, the effects of coating structure on the improvement in flowability are not yet fully understood. Thus, predicting the improvement resulting from this technique is difficult. In this study, we focused on the effects of the particle diameter distribution of the admixed particles on coating structures and improvement of flowability in terms of the compacted packing fraction in a particle bed. Main particles of size 397 nm with admixed particles of sizes 8 and 104 nm were used. Bimodal particle diameter distributions were adjusted by changing the mixing ratios of the two admixed particles. Furthermore, the main and admixed particles were mixed in various orders. We examined the compacted packing fractions for these different mixing ratios and orders. Scanning electron microscopy images were obtained in order to analyze the coating structures on the main particle surfaces. The results show that the main particle packing fraction was most greatly improved by pre-mixing the two admixed particles. This can be explained by a linked rigid-3-bodies model with leverage based on increasing the apparent diameter of the main particles. (C) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.