In this study, kaolinite/epoxy resin nanocomposites were fabricated using functionalized kaolinite (KGS) as filler. The KGS was prepared by silylation of 3-aminopropyltriethoxysilane onto the surface of mechanically ground kaolinite. The addition of KGS into epoxy resin matrix improved the storage modulus and glass-transition temperature, compared to those of epoxy resin nanocomposites filled with raw kaolinite. Furthermore, with the increase of KGS loading, the coefficient of thermal expansion decreased gradually, and the dielectric constant slightly increased when compared to that of pure epoxy resin. The presence of kaolinite led to an improvement in the water resistance property of kaolinite/epoxy resin nanocomposites. This research provided guidance to construct high-performance kaolinite/epoxy resin nanocomposites.