Recently, high entropy alloy (HEA) concept has been studied as a means of achieving excellent properties of metallic alloys. We have developed an HEA alloy through powder metallurgy, which possesses both high strength and large ductility (as large as 70% at room temperature). However, currently the knowledge at the microstructural scale concerning the underpinning mechanisms during deformation are limited, especially with respect to the interaction between local strain hardening and grain defects (e.g. dislocation substructures and twins). In order to determine these, we proposed to use neutron diffraction to quantify the evolution of the lattice strain in situ during tensile deformation. The results in concert with ex situ electron microscopic characterizations currently undergoing, will provide a pathway for designing HEAs with both enhanced strength and superior ductility.