Abstract: The exfoliated epoxy resin/MMT nanocomposites were prepared by preexfoliated method, and the effect of montmorillonite on microstructure and mechanical properties of epoxy resin were studied by XRD, SEM and DMA. Experimental results showed that it’s good for preparing exfoliated epoxy resin/MMT nanocomposites to preexfoliate montmorillonite before curing epoxy resin E53. Due to the addition of montmorillonite, the T_g of epoxy resin/MMT nanocomposites was about 5 ℃~8 ℃ higher than that of the epoxy resin. The storage modulus and stiffness of the epoxy resin increased with the increasing of T_g, and lower β transformation temperature made the best low temperature toughness. So exfoliated inorganic nanosheets can effectively prevent cracks along the exhibition, and play the role of reinforcing and toughening in epoxy resin/MMT nanocomposites.