Next-generation electronics require mechanical flexibility and durability as well as electrical conductivity. In this report, few-layer graphene and polyelectrolytes were assembled into ultrathin films on flexible plastic substrates by a simple and cost-effective layer-by-layer technique. This technique integrated high electrical conductivity and excellent oxygen barrier property into a single film. These characteristics have been rarely reported for other types of thin films prepared by solution processing. The optical properties, film thickness, and mass of the films were precisely controlled by the number of bilayers. After a brief exposure to nitric acid (HNO3) vapor, the films exhibited much improved electrical conductivity while preserving their other properties. Raman, x-ray photoelectron, and FT-IR spectroscopy proved that the effects of the HNO3 treatment were due to the removal of polymeric components and restricted to the film surface, and not due to the chemical doping of graphene. (C) 2017 Elsevier Ltd. All rights reserved.