Abstract: Carbon nanotubes (CNTs) were respectively treated by mixed acid, epoxy resin (EP) and silane coupling agent. Montmorillonite (MMT) was modified by eighteen alkyl three methyl ammonium chloride. CNTs and organic montmorillonite (OMMT) were placed in EP cured by anhydride. Nano OMMT/EP, CNTs/EP and CNTs-OMMT/EP composites were prepared by method of solution blending. The impact strength of the three kinds of was tested by Charpy impact tester. The impact profile of the nano CNTs/EP, OMMT/EP and CNTs-OMMT/EP composites were observed by scanning electron microscopy. The experimental results show that when the mass fraction of OMMT is 4wt%, the impact strength of OMMT/EP composites is 16.7% higher than that of the pure EP. The interface between Si-CNTs and EP cured by anhydride is strong. When the mass fraction of Si-CNTs is 0.9wt%, the impact strength of Si-CNTs/EP composites is 84.0% higher than that of the pure EP. When the mass fraction of OMMT is 4wt% and the mass fraction of CNTs is 0.9wt%, the impact strength of Si-CNTs-OMMT/EP composites is 135.4% higher than that of the pure EP. CNTs and OMMT can synergistically enhance the toughness of EP.