Medium-Mn steel typically alloyed with (3%~10%)Mn (mass fraction) has recently regained significant interest as one of the most promising candidates for the third-generation automobile steel due to its excellent combination of ultra-high strength and ductility as well as relatively low material cost and industrial feasibility. Considering the ever increasing strength level as well as the comparatively high amount of reverted austenite (RA) of medium-Mn steel, special attention began to be given to its hydrogen embrittlement (HE) behavior for ensuring the safety service of components made of this kind of steel. However, the effect of RA on HE of medium-Mn steel has not been fully understood. For this purpose, the susceptibility to HE of a cold-rolled medium-Mn steel 0.1C-5Mn intercritically annealed at 650 ℃ for different time to obtain different amounts of RA was investigated by using electrochemical hydrogen charging, thermal desorption spectrometry (TDS), slow strain rate test (SSRT) and SEM. The results show that the annealed samples exhibit a dual-phase microstructure of reverted globular shaped RA and ferrite. The ultimate tensile strength (σ_b) increases while the yield strength decreases with increasing annealing time, and both the total elongation (δ) and the product of σ_b to δ (σ_b×δ) initially increase and then decrease with increasing annealing time. That is to say, an excellent combination of strength and ductility could be obtained when the tested steel was annealed at 650 ℃ for 10 min. However, the results of TDS and SSRT show that both the absorbed diffusible hydrogen concentration and the susceptibility to HE increase with increasing annealing time, and the latter is more significant. SEM analysis of the fracture surfaces of fractured samples revealed that the hydrogen-charged annealed sample was fractured to leave both dimples filled with grains and empty dimples while the uncharged annealed specimen was ductile fractured to leave only empty dimples. The dimples filled with grains were basically a brittle intergranular cracking occurring along the boundaries of RA and/or martensite (formerly RA) grains by the hydrogen-assisted cracking mechanism. It is thus concluded that the HE behavior of intercritically annealed cold-rolled medium-Mn steel is primarily controlled by both the amount and mechanical stability of RA.