Nanocomposites with carbon-based fillers have been widely investigated due to unique properties derived from the extended interface between the polymer matrix and the filler. In particular, many studies have been focused on GO reinforced nanocomposites showing relevant improvements of physical and mechanical properties. Recently we reported the dual role of graphite oxide (GO) in epoxy resin thermosets exerted as catalyst on the reaction between the epoxy and amine groups of the resin, which leads to higher crosslinking density in milder conditions, and as filler for the nanocomposite.[1] A dual role of graphite oxide was also found for polyester resins. In fact, GO is effective to promote the polymerization reaction from the starting monomers, like diethyl fumarate and ethylene glicole, to give prepolymers suitable for the subsequent curing step. The chemical functionalization of GO during the polymerization assures a better dispersion reducing the possible nanofiller aggregation. [1] M.Mauro, M. R. Acocella, C. Esposito Corcione, A. Maffezzoli, G. Guerra Polymer 2014, 55(22), 5612-5615