Increasing production of graphene-based nanomaterials (GBMs) such as graphene oxide (GO) and reduced graphene oxide (rGO) raises the question of potential adverse outcomes on living organisms and especially toward microorganisms constituting the basis of the trophic chain in ecosystems. Evaluation of the GBMs toxicity were performed on various microorganisms using single species while the characterization of toxicological effects of GBMs towards more complex communities is lacking. This study focuses on the ecotoxicological assessment of GO and rGO towards a biofilm composed of the diatom Nitzschia palea associated to a bacterial consortium under controlled conditions.