Abstract: The multi-walled carbon nanotubes (MWCNTs) were functionalized to produce oxidized MWCNTs (MWCNTs-COOH) and epoxidized MWCNTs (MWCNTs-Epon828). Three types of Graphene-MWCNTs/EP composites were prepared by adding the graphene sheets and different types of MWCNTs into the epoxy resin (EP), respectively. By means of tensile test and thermal gravimetric analysis, the synergetic effects of graphene and MWCNTs, the effects of their content and the methods of MWCNT functionalization on the mechanical and thermal properties of the composites were studied. The results indicate that the synergetic reinforcement of the graphene and MWCNTs has a better performance than that of sole MWCNTs. Even with 0.1% mass fraction of the graphene and MWCNTs, the tensile strength of Graphene-MWCNTs-Epon828/EP composite approaches the ultimate value: The tensile strength, elastic modulus, and the elongation at break have been increased by 35%, 65% and 34%, compared with the pure EP, respectively. The thermal stability of all the Graphene-MWCNTs/EP composites are improved with the addition of graphene and MWCNTs.