In recent years, increasing attention has been paid to the effect of a hydrogen environment on the fatigue limit of hydrogen-power systems and infrastructure. In carbon steel, strain aging is one of the important factors influencing non-propagating crack behavior, which is related to the fatigue limit. In the present study, to investigate the effects of hydrogen on the strain aging of low-carbon steel (0.13 % carbon steel), Vickers hardness tests were carried out on the carbon steel. A couple of 0.13 % carbon steel specimens with a large-scale plastic zone were aging heat-treated; one was a hydrogen-charged specimen, whereas the other was an uncharged specimen. The Vickers hardness of the hydrogen-charged specimen was found to be lower than that of the uncharged specimen. This observation implies that hydrogen inhibits strain-aging hardening of low-carbon steel. The observation also suggests that hydrogen could affect the non-propagating crack behavior through the inhibition of strain aging.