This paper aims to investigate the effect of hydrogen-induced mechanical degradation of low carbon steel at macro-, micro- and nano-levels in the hydrogen-rich acidic environments. From the test results of specimens, a relationship in hydrogen concentration and corrosion propagation was observed that led to the significant reductions of bulk elastic modulus after 28 days of exposure to the hydrogen-rich acidic environments. Through microstructural analysis, the deformation of larger grains, cracks, and blisters caused by hydrogen penetration was found as the possible cause for this reduction. Moreover, by performing nanoindentation on the areas of interest of various specimens at planned time periods, the influence of hydrogen on the nano-elastic and nano-hardness properties of grains was determined. The 3D surface profiles of the nano-elastic modulus and nano hardness of various specimens are presented in this paper. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.