Substitution of Ge for Mn increases the elastic moduli of different {h k l} orientations of the CoCrFeMnNi-based high-entropy alloy. Our findings indicate that tuning minor element compositions may result in improved strength-ductility combination. The underlying deformation mechanisms of CoCrFeNiGe(0.3)were examined byin situneutron diffraction and analysis of the associated diffraction profiles during tensile deformation. The strain-hardening response of CoCrFeNiGe(0.3)exhibited a dominant mechanism of mechanical twinning at moderate and large strains at room temperature. The evolution of the bulk work hardening rate was consistent with the convolutional multiple whole profile fitting results, which exhibited a continuous increase in twin formation probability. The microstructural development was also investigated by transmission electron microscopy, which revealed the formation of huge amounts of deformation twins in CoCrFeNiGe(0.3)at room temperature.