In this research, flexure, Mode-I, and Mode-II strengths, as well as the interlaminar shear strength (ILSS), of Kevlar fiber/epoxy composites are tested, as are the effects of adding silane-treated nano-CaCO 3 particles. The silane coupling agent 3-Glycidyl oxy propyl trimethoxy silane (GPTMS) can be used to modify the surface of nanoCaCO 3 particles. Some of the tests performed on the composite samples include three-point bending, double cantilever beam (DCB), end-notch flexure (ENF), and short beam shear, all of which are mandated by the applicable ASTM standards. Experimental results show that when silane-treated nano-CaCO 3 particles make up 5 % of the composite’s weight, the flexural modulus, flexural strength, Mode-I fracture toughness, Mode-II fracture toughness, and ILSS values are improved by 17.2 %, 14.2 %, 26.3 %, 20.1 %, and 20.4 %, respectively, when compared to reference composites. When silane is applied to nano-CaCO 3 particles, they gain 15.3 % in storage modulus. The composites’ glass transition temperature was little impacted by the incorporation of silane-treated nano-CaCO 3 particles.