Mechanical properties of Fe–20Mn–(10–14)Al–(0–1.8)C (mass%) quaternary and Fe–20Mn–(10–14)Al–(0.75–1.8)C–5Cr (mass%) quinary alloys were investigated by hardness, cold-workability and tensile tests at room temperature. The γ(fcc) alloys in both quaternary and quinary systems with a low density of less than 7.0 g/cm³ showed an excellent ductility and their hardness and tensile strength increased with increasing Al and C contents. The γ+α(bcc) duplex alloys also exhibited a high tensile strength by controlling the α volume fraction. TEM observation confirmed that high hardness and tensile strength of the alloys with high Al and C contents are caused by the precipitation of nano-size κ-carbide with perovskite structure during cooling from the annealing temperature. Fe–20Mn–11Al–1.8C–5Cr alloy with a density of 6.51 g/cm³ showed a high specific strength of more than 180 MPa·cm³/g with a good tensile elongation of 40%. The present Fe–20Mn–Al–C(–5Cr) alloys showed a higher specific strength than conventional steels.