This study explores the periodic spinodal decomposition in a ferrous medium-entropy alloy (Fe-MEA) to enhance its strength and ductility. By introducing small amounts of Cu and Al, the alloy undergoes nanoscale periodic spinodal decomposition through a one-step aging process. This process induces spinodal hardening, leading to a significant increase in strength without compromising ductility. The periodic spinodal decomposed structures effectively overcome strain localization issues, preserving elongation while doubling the mechanical strength. The study demonstrates that spinodal decomposition, a spontaneous process with minimal elemental addition, offers a promising approach for enhancing the mechanical properties of advanced alloys, particularly in high/medium entropy alloys (H/MEAs). The findings highlight the potential of spinodal hardening as an advanced paradigm in alloy design, providing a foundation for developing next-generation metallic materials with improved performance.This study explores the periodic spinodal decomposition in a ferrous medium-entropy alloy (Fe-MEA) to enhance its strength and ductility. By introducing small amounts of Cu and Al, the alloy undergoes nanoscale periodic spinodal decomposition through a one-step aging process. This process induces spinodal hardening, leading to a significant increase in strength without compromising ductility. The periodic spinodal decomposed structures effectively overcome strain localization issues, preserving elongation while doubling the mechanical strength. The study demonstrates that spinodal decomposition, a spontaneous process with minimal elemental addition, offers a promising approach for enhancing the mechanical properties of advanced alloys, particularly in high/medium entropy alloys (H/MEAs). The findings highlight the potential of spinodal hardening as an advanced paradigm in alloy design, providing a foundation for developing next-generation metallic materials with improved performance.