High Entropy Alloys (HEAs) are in the focus of materials science due to their high strength, good ductility and excellent resistance to wear, corrosion and softening at high temperatures. HEAs are disordered solid solutions, containing at least five chemical elements with similar concentrations. The goal of our study was to investigate the influence of plastic deformation on the microstructure and hardness of the HEAs. The evolution of the grain size and the dislocation density was studied by electron microscopy and X-ray line profile analysis. We have investigated the relationship of the mechanical behaviour, the microstructure evolution and the dislocation density in High-Entropy Alloy after plastic deformation.