In this work, Y2O3/Cr2O3 composite coatings were deposited on 316 L stainless steel by metal organic chemical vapour deposition (MOCVD). Effect of Cr2O3 layer on the microstructure, mechanical properties and deuterium permeation properties of Y2O3 coating was investigated. In order to investigate the evolution of the microstructure in working environment, Y2O3/Cr2O3 composite coating was high temperature annealed in argon or hydrogen atmosphere. After annealing at 973 K in hydrogen atmosphere, the (222) diffraction peak became weak whereas the (400) diffraction was strengthened. The adhesion force reduced from 9.7 N of the Y2O3/Cr2O3 composite coating annealed in argon atmosphere to 8.6 N of that annealed in hydrogen atmosphere. It was inferred that hydrogen atoms invasion might be responsible for this mechanical property difference. The deuterium permeation inhibition performance of the coatings was examined by deuterium permeation measurement. After annealed at 973 K in argon atmosphere, the single-layer Y2O3 coating exhibited the minimum reduction in deuterium permeability, and the permeation reduction factor (PRF) values were in the range of around 435-272 at 873 973 K. The maximum reduction in deuterium permeability was obtained from the Y2O3/Cr2O3 composite coating with Cr2O3 layer thickness of 120 nm, and the PRF values were in the range of around 612-432 at 873-973 K. With further increasing thickness of the Cr2O3 layer to 160 nm, the hydrogen permeation inhibition performance of the composite coating lowered instead. Furthermore, the Y2O3/Cr2O3 composite coating annealed in argon atmosphere exhibited better deuterium permeation inhibition performance than that annealed in hydrogen atmosphere. After adding the Cr2O3 layer, the Y2O3/Cr2O3 coating exhibited stable permeation fluxes at each driving pressure, while spikes of the permeation flux were observed for the single-layer Y2O3 coating. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.