Lightweight medium-manganese steels are attracting more focus in automotive industry with excellent mechanical properties due to austenite-reverted-transformation annealing process. In this study, hydrogen embrittlement behavior of medium-manganese steel was investigated via a novel in-situ hydrogen charging combined with nanoindentation. Besides, postmortem analysis using high-resolution microstructural characterization methods: scanning electron microscopy (SEM), electron back-scattered microscopy (EBSD) were performed. Different hydrogen responds of both reverted austenite and ferrite were studied and will be reported. ed.