In this paper, poly (m-xylylene adipamide-terephthalyl amide) (MXD6T) and silicon dioxide (SiO2) nanocomposite with SiO2 load from 5% to 20% (by mass) is prepared and used to improve the barrier property of polyester bottle materials. In preparing MXD6T-SiO2 (NMXD6T), silica is in-situ polymerized with hexane diacid, terephthalic acid (TPA), alkyl and aromatic diamine. The different molar ratio of hexane diacid to terephthalic acid with the same molar diamine is designed to give the composites with different viscosity, thermal performance and the barrier properties. The 3-8 times of enhanced permeability of these polyester matrix nanocomposites with this NMXD6T to pure polyester resins are reported. The relationship of NMXD6T’s configuration and the permeability properties of polyester nanocomposites are characterized. DSC shows that NMXD6T is totally amorphous. FTIR shows the existence of silicon-oxygen bond formed in the nanocomposite, and TEM indicates an average size from 30nm to 100nm of SiO2 particles being phase separated from MXD6T matrix, while well bonded to the polyester chains.