In situ potentiostatic and photoelectrochemical measurements were employed concurrently to investigate the effects of hydrogen on the properties of the passive films on X70 microalloyed steel. The photocurrent of the passive film increases with film formation time and reaches a steady value after a long time of passivation. After a steady-state current was attained, the hydrogen charged into the specimen resulted in an increase in the anodic current density of the film, which then resumed to the steady state after the hydrogen charging was cut off. Nevertheless, concurrent photoelectrochemical experiments revealed that the photocurrent of the film was also enhanced by hydrogen, but the photocurrent did not undergo recovery to the initial value before hydrogen charging, which is contrary to the result obtained for the anodic current after the cessation of hydrogen charging. The discovery of the irreversible effect of hydrogen on the photocurrent of the passive film is first reported by this team. © 2005 The Electrochemical Society. All rights reserved.