The excellent mechanical properties of medium Mn steels have been widely recognized, but there exists a problem in their stretch flangeability, which limits the wide applications of medium Mn steels in practical production. In this study, the microstructures, mechanical properties and stretch flangeability of two medium Mn steels with compositions of 0.2C-8Mn-0/3Al (wt.%) were systematically investigated. It is indicated that the microstructure consists of ultrafine austenite and ferrite grains in both Al-free and Al containing alloys and the stability of austenite increases with an increase of Al concentration. The research results show that the Al containing alloy can achieve higher ductility while ensuring high tensile strength (>1000 MPa). The total elongations of Al-free steel and Al-containing steel annealed at different temperatures in the two-phase regions were in the range of 11% ~ 44% and 20% ~ 50%, respectively. More importantly, the hole expansion ratio of the experimental steel was nearly doubled (~90%) by adding Al element. The higher total elongation and excellent stretch flangeability of the experimental steel with Al addition can be attributed to the dual contribution of the TRIP effect and the coordinated deformation of fully recrystallized ferrite. In contrast, due to the lower annealing temperature, the Al-free experimental steel retained considerable incompletely recrystallized ferrite grains with a higher dislocation density, and there is difficulty in coordination in the deformation process.