In this study, the effects of C and Si on damping capacity and mechanical properties of as-cast and as-rolled Fe-17%Mn alloys were investigated as a basic study for the purpose of the commercialization of the alloy. The M_(S) temperature of γ→ε martensitic transformation in Fe-17%Mn alloy was decreased with increasing C and Si contents, resulting in the less volume fraction of a martensite. The damping capacity was also decreased with increasing alloying content because of less s amount and the reduction in mobility of the damping sources such as the stacking fault boundaries and γ/ε interfaces due to the pinning effect by alloying elements. The mechanical properties of as-rolled alloys were superior to those of as-cast alloys probably because of finer γgrains, larger amount of ε martensite, and chemical homogeneity.