Effects of Mn content on mechanical properties of FeCoCrNiMnx (0 ≤x ≤ 0.3) high-entropy alloys (HEAs) are investigated via first-principles calculations combining EMTO-CPA method.Related physical parameters,including lattice constant,elastic constants,elastic modulus,Pugh's ratio,anisotropy factors,Poisson's ratio,Cauchy pressure,Vickers hardness,yield strength,and energy factor,are calculated as a function of Mn content.The results show that the resistances to bulk,elastic,and shear deformation decrease with increasing Mn content.Pugh's ratio B/G indicates that the ductility of FeCoCrNiMnx HEAs has a remarkable reduction between 22 and 24％ of Mn content.Meanwhile,Cauchy pressure suggests that the atomic bonding transforms from metallic to directional characteristic from 22 to 24％ of Mn content.Vickers hardness and yield strength of FeCoCrNiMn HEA are intrinsically larger than those of FeCoCrNi HEA.Dislocation nucleation easily occurs in FeCoCrNiMn HEA compared to FeCoCrNi HEA,and large dislocation width in FeCoCrNiMn0.2 HEA results in low stacking-fault energy,which easily induces twinning deformation.This work provides a valuable insight for further theoretical and experimental study on the mechanical properties of FeCoCrNiMnx (0 ≤ x ≤ 0.3) HEAs.