CoCrFeMnNi high-entropy alloy (HEA) materials were fabricated using mechanical alloying (MA) and spark plasma sintering (SPS). The MA time, SPS temperature, and contaminations strongly affected the final microstructure and mechanical properties. Nanocrystal face-centered cubic (FCC) solid solution was made during MA, and the FCC phase maintained as the matrix after SPS at 900 °C and 1100 °C. However, Cr carbides were transformed near the surface due to the carbon contamination. When MA time increased, phase stability of the FCC phase was improved, and the contaminant (ZrO2) from the MA balls was also increased. Ultrafine-grained microstructure was obtained at 60 min MA and 900 °C SPS. On the other hand, the higher SPS temperature and lower levels of contamination were required to achieve tensile ductility. Irregularly distributed ZrO2 particles developed bimodal microstructures. Display omitted •CoCrFeMnNi high-entropy alloys were fabricated using powder metallurgy.•Contaminations highly affected microstructural evolution and mechanical properties.•Phase stability was improved with increasing ball milling time.•UFG microstructure was obtained under a certain condition.