The effect of hydrogen and stress on the phase transformation and surface cracking in cold-rolled and annealed AISI 304 stainless steels was investigated. Hydrogen was introduced by cathodic charging in 0.1 M H2SO4 + 1 g/L Na2HAsO4 center dot 7H(2)O. Scanning electron microscopy was used to observe structural changes and surface cracks of the specimens. X-ray diffraction analysis was used to investigate phase transformations in the uncharged and charged specimens immediately after charging or during aging. Cathodic charging can cause epsilon martensite phase transformation and aging after cathodic charging can induce the epsilon and alpha' martensite transformation. There are a certain amount of surface cracks on the specimens surface after hydrogen charging or during aging. The surface morphology of the specimens is studied, and the mechanism of the hydrogen-induced phase transformation and the surface cracking formation in the charged specimens immediately after charging or during aging is discussed. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.