In this research, high entropy alloy CoCuFeMnNi was prepared using VIM furnace. Next, in order to identify the transformation temperatures of this high entropy alloy, DSC thermal analysis was taken from it, and the results obtained from this analysis indicated heat change at temperatures of 566, 891 and 1064 ^oC. To study thermal changes based on microstructure, samples of high entropy alloy CoCuFeMnNi were heated at temperatures determined from DSC analysis and then quenched in water. The aim of this operation was to stabilize the microstructure during heat treatment. Then the quenched samples were analyzed by XRD analysis. The results of phase analysis revealed that the samples heat-treated at 566 ^oC contain a new phase that precipitated and started to dissolve in the original phase as the temperature increased to 1064 ^oC. In this regard, the samples were subjected to metallography and microstructure analysis and elemental evaluation using optical microscope and SEM, respectively. The obtained OM and SEM images and results indicated that with the increase in heat treatment temperature, the Diffusion of copper from the dendritic phases (copper-rich phase) to the base increased and as a result, the fraction of dendritic phases decreased, which is more evident at the temperature of 1064 ^oC.