Fe-15Mn-10Cr-8Ni-4Si is a newly developed alloy for seismic damper applications. The low- and high-cycle fatigue (LCF and HCF) properties of this alloy was investigated in this study. The LCF resistance of this alloy was found to be superior to that of other materials. The inelastic component was established to be the main contributor to the superior fatigue life of Fe-15Mn-10Cr-8Ni-4Si, including at relatively low strain levels. This alloy demonstrated a gradual and mild cyclic hardening behavior at a wide range of strains. In terms of the HCF property, the fatigue limit was 262.5 MPa, which is 96% of 0.2% proof stress of 274 MPa. A surface observation of the post-fatigued specimen tested at a stress amplitude of 250 MPa for 107 cycles without failure showed that while surface relief developed, no cracks with a size of at least several grains were detected. Since Fe-high Mn alloys generally exhibit several unique deformation modes involving the deformation-induced phase transformation, the microstructure of Fe-15Mn-10Cr-8Ni-4Si after fatigue was investigated using electron-backscatter diffraction (EBSD) microscopy. As a result, ε-martensite formed via the deformation-induced γ→ε martensitic transformation was detected in all specimens tested under different conditions. Even at a stress level lower than the fatigue limit, ε-martensite formed while the amount of it was very limited. Except for the specimen tested at a low stress level of 275 MPa, a well-developed deformation-induced microstructure was found near the crack; α′-martensite formed by the two-stage phase transformation γ→ε→α′ was detected only in the region near the crack in a specimen tested at a total strain range of 2%.