The single-phase face-centered cubic (fcc)-structured Fes0Mn27Ni10Cr1 3 high entropy alloy (HEA) exhibits good ductility but low strength,which presents a challenge.By Mo-alloying and thermomechanical treatments,we have designed the (Fes0Mn27Ni10Cr13)100-xMOx (x=0-6 at.％) alloy series with a wide range of mechanical properties.The careful control of secondary phases introduced in the cold-rolled and annealed (Fe50Mn27Ni10Cr13)Mo2 sample resulted in an enhanced tensile strength from 250MPa to 665 MPa,still having ～25 ％ ductility.TEM investigations of this alloy revealed the presence of deformation twins,dislocation cells,and ordered bcc nano-particles embedded in the ductile fcc matrix post-deformation.The observed deformation structures are an indication of successful cooperation between deformation twinning and precipitation strengthening in enhancing the tensile strength at maintained ductility compared to its cast counterpart.This work provides insight into the tunability of the mechanical properties of non-equiatomic HEAs via alloying and thermomechanical processing.