Abstract: Cold-rolled low-carbon medium-manganese steel (0.2C-5Mn) was cooled by different methods after annealing. Its microstructure and tensile properties were investigated by means of tensile testing, scanning electron microscopy (SEM), electron back scattered diffraction (EBSD), transmission electron microscopy (TEM), and X-ray diffraction. Intercritical annealing after cold rolling results in a duplex structure of ultrafine ferrite and reverted austenite. Reverted austenite in the steel experienced annealing and air cooling is more stable and its volume fraction is significantly higher than that in the steel treated by annealing and furnace cooling. In addition, reverted austenite in the steel experienced annealing and air cooling can produce sustained TRIP effect during deformation, leading to improvements in strength and plasticity. The product of tensile strength and total elongation exceeds 26.5 GPa.%.