Composite coatings as Hydrogen Isotopes Permeation Barriers have seldom been studied. In this work, the Al2O3-Er2O3 component composite HIPB were prepared on 316L stainless steel by radio frequency reactive magnetron sputtering. The deuterium permeation reduction factor (D-PRF), structure and nano-hardness of the Al2O3-Er2O3 composite HIPB were investigated. The Er4Al2O9 (012), (023) diffraction peaks appeared. The D-PRF of 1.2 mu m Al2O3-Er2O3 composite HIPB could reach 160 at 600 degrees C, the D-PRF was 210 at 450 degrees C and increased sharply to 1380 at 250 degrees C. The coatings kept dense during the deuterium permeation tests while the Er4Al2O9 phases changed. The nano-hardness decreased from 9.55 GPa to 7.46 GPa after the deuterium permeation tests. It was inferred that the deuterium atoms invasion and formation of oxygen vacancies should be responsible for the performance and structure changes of the Al2O3-Er2O3 composite HIPB during deuterium permeation tests. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.