The influence of severe plastic deformation on the high-entropy alloy CoCrFeMnNi in equiatomic composition („Cantor alloy“) was investigated. Severe plastic deformation was achieved using high-pressure torsion (HPT). As characterization methods microhardness testing, tensile testing, electron microscopy, x-ray diffraction and atom probe tomography were used. A saturation effect regarding the grain refinement during the HPT-process was observed. The saturation grain size was approximately 50 nm. The significant grain refinement leads to an increase in hardness by approximately a factor of three for the investigated alloy. Isochrone heat treatments (t =1h) revealed that annealing temperatures between 100°C and 550°C resulted in an increase in the materials hardness and the hardness maximum occurred at 450°C. Isothermal heat treatments at 450°C lead to a further increase in hardness, the maximum of approximately 910HV1 was reached for an annealing time of 100h. A combination of transmission electron microscopy as well as 3-dimensional atom probe tomography was used in order to find an explanation for this effect. The results showed that for annealing temperatures of 450°C a decomposition of the single-phased high-entropy alloy and the formation of intermetallic phases occurred. The occurrence of new phases (η‘‘, α1 and a Cr-rich phase) also was verified using analysis via x-ray diffraction. Furthermore the influence of severe plastic deformation und subsequent heat treatment on the tensile properties of the CoCrFeMnNi alloy was investigated. Especially for an annealing temperature of 450°C a significant embrittlement of the material occured. For annealing temperatures higher than 600°C a significant increase in ductility was observed.