Abstract: The present invention pertains to a process for producing a composition comprising graphene and at least one polymer, and especially for producing a graphene-filled polymer nanocomposite. Specifically, the present invention resides in a process for manufacturing a composition comprising graphene and at least one polymer, the process comprising the steps of: (i) providing an aqueous suspension of graphene [dispersion (G)]; (ii) mixing the dispersion (G) with an aqueous polymer latex to obtain a liquid mixture [mixture (M)]; and (iii) co-coagulating the mixture (M) to obtain said composition. The graphene-filled polymer nanocomposites made by the process of the present invention have advantageously shown excellent barrier properties, indicating a nearly homogenous and sufficiently scattered filler distribution in the base polymer.