This study fabricates a transparent cyclic olefin copolymer (COC)/thermally reduced graphene oxide (TRGO) composite film with low content of TRGO, which exhibits high water vapor barrier properties. With only 0.06 wt% (0.028 vol%) TRGO, the COC/TRGO composite film reduces the water vapor permeability by similar to 21%. The amount of TRGO in this work is 10-100 times lower than that in other polymer/clay or polymer/graphene composites that reduce the water vapor permeability at the same percentage. Low TRGO content has benefits of fabricating a film with low cost, high transparency, and truly excellent flexibility. The water vapor permeabilities of COC/TRGO composites are much lower than those predicted by Cussler or Nielsen model because of the significant rigidification of COG chains near TRGOs. The COC/TRGO composite film was annealed at different temperatures and then surface modified with amphiphilic polymer to further improve its barrier performance. By treating the film with 0.06 wt% TRGO, the water vapor permeability is greatly reduced by similar to 65%. (C) 2015 Elsevier Ltd. All rights reserved.