The concept of nanoscale reinforcement provides opportunity for synthesis of new polymer materials with unique properties. Montmorilonite (MMT) was derived from bentonite, purified, activated by sodium ions and mixed with reacting unsaturated polyester (UP). X-ray and transmission electron microscopy data were in support of the formation of a partially delaminated nanocomposite material. At an MRT content of only 1.5 vol%, the fracture energy, G(Q), of the nanocomposite was doubled, 138 J/m(2) as compared with 70 J/m(2) for the pure UP.