Particle gradation effect on the shear-dilatancy of granular soils was studied through a series of drained triaxial tests using the discrete element and finite difference methods (PFC3D-FLAC3D). Spherical particles with different coefficients of uniformity Cu and median particle sizes D50 were assembled to exclude the strong size-shape correlation in natural sands. Four groups of Cu and four groups of D50 at the same void ratio ecprior to shearing, and seven more groups with the same void ratio e0 prior to isotropic compression were tested. Various mechanical behaviors were analyzed, including the stress-strain response, the stress-dilatancy response, friction angle, and fabric anisotropy. Cu significantly influences the peak friction angle, the maximum dilation angle, and the anisotropies of normal contact force and contact normal, whereas these are almost independent of D50. The contribution of the maximum rate of dilation to the excess friction angle is largely independent of Cu and D50 for spherical particles. (c) 2024 The Society of Powder Technology Japan. Published by Elsevier BV and The Society of Powder Technology Japan. All rights are reserved, including those for text and data mining, AI training, and