Abstract In this work, chemically modified sodium montmorillonite and epoxy monomer were used to prepare nanocomposites in two consecutive stages. In the first stage, dodecylamine, octadecylamine, hexadecylamine, and hexadecyltrimethyl ammonium bromide were used to prepare various organophilic clays. In the second stage, the bisphenol‐A based epoxy monomer and predetermined amounts of organoclay were mixed together and then cured by an aliphatic polyamine for 20 min under microwave at 400 W. Furthermore, α‐ω diacrylate poly(dimethylsiloxane) was added to the mixture before the curing process to modify the toughness of the samples. The mixture was poured into the poly(tetrafluoroethylene) mold; the epoxy resin/curing agent ratio was maintained as 2/1. The clear films formed after microwave irradiation were removed from the mold, cooled, and then stored in a cool and dry medium until characterization. The samples were analyzed by wide angle X‐ray diffraction, differential scanning calorimetry, and mechanical tests. Surfaces of the cold fractured samples were also observed under the scanning electron microscope. The results revealed that microwave curing of the samples of 5% organoclay and 5% siloxane showed improvement in mechanical properties. POLYM. ENG. SCI. 46:1104–1110, 2006. © 2006 Society of Plastics Engineers