The microstructures and tension properties of Fe50Mn20Cr20Ni10 medium entropy alloy (MEA) were investigated, which was produced by vacuum induction melting and subsequently was homogenized at 1200 C for 6 h. Microstructure characterization shows the single-phase solid solution with face-centered cubic structure by means of transmission electron microscopy and scanning electron microscopy combined with energy disperse spectroscopy. Our Fe-MEA has an ultimate tensile strength of 550 ± 10 MPa and a high strain hardening exponent, n, of 0.41 as well as a higher ductility (60%) than those of CrMnFeCoNi alloy. The single-phase solid solution deforms plastically via dislocations and twins. Twin boundaries associated with deformation twinning impede dislocation motion, enhancing the strain hardening capacity. This article focuses on the insights into the concept of Fe-MEAs and provides a potential direction for the future development of high entropy alloys and MEAs.