A facile synthetic method was developed to prepare polyelectrolyte complex/graphene oxide nanocomposite membranes with biomimetic brick-and-mortar structures, in which their tensile strength and modulus were improved 3 and 1.5 times with a loading of 1.5 v% of graphene oxide, reaching 115 MPa and 3.5 GPa, respectively. Oxygen permeation of PEC@GO films was reduced by 4 orders of magnitude, due to the layered arrangement of GO in the PEC matrix.