This paper examines the potential influence of particle-size distribution on stress-dilatancy behavior of granular materials from the results of 35 conventional drained triaxial compression tests. Seven different grain-size distribution curves of two different materials (glass beads and Péribonka sand) in the range of 63–2,000 µm were tested at different normal pressures and initial relative densities. It was shown that for a given relative density and confining pressure, although shear strength and volumetric response of the tested materials were independent of the coefficient of uniformity, $C_u$ , in the investigated range, they were significantly influenced by the variation of the mean particle size, $D_{50}$ . On the basis of the triaxial test results, a correlation between the material constant $\alpha$ of a modified stress-dilatancy equation and D₅₀ of the tested materials was found. In addition, the coefficient of an equation, which was introduced as an experimental adjustment of the well-known stress-dilatancy equation, were fine-tuned to account for $D_{50}$ . A comparison of the predictions by the proposed empirical formulas with stress-dilatancy data from the literature and a micromechanical explanation of the experimental results are also provided.