AbstractFourier transform infrared spectroscopy (FT‐IR) has been utilized to investigate the interfacial chemical bonding at the interfaces of the aminosilanes and the nedic methyl anhydiride cured epoxy matrix in fiber‐reinforced composites. It is found that the nedic methyl anhydride can react with γ‐aminopropyltriethoxysilane (APS) and N‐methylaminoproplytrimethoxysilane (MAPS). In comparing the relative reactivities of two coupling agents to the epoxy resin, the secondary aminosilance has a higher reactivity than the primary aminosilance. An elevated temperature is required for the copolymerization to take place between the silane and the epoxy resin. The results indicate that covalent bonds form at the coupling agents. The molecular structure of the interface in MAPS treated fiberglass reinforced composites is different from that of the APS treated fiber composites. In addition, an accelerated copolymerization initiated by the coupling agent treated surface is also found in the resin interphase which may be important in determining the mechanical properties of the co