This work has consisted in studying the effect of the particle size distribution and the added quantity of a kaolin on the tensile mechanical behavior of an epoxy resin. The obtained results have allowed to highlight that a fine particle size distribution of kaolin incorporated in a small proportion (10%) is favorable both to a high stress to rupture and an improved Young’s modulus. When the amount is 20%, the mechanical performance is affected because of the presence of interfacial decohesions (defects) between the larger agglomerates and the matrix.