A group of Al-Co-Cr-Fe-Ni alloys was synthesized for diffusion couple experiments that were performed in the temperature range of 1273–1373 K. The measured concentrations profiles were used to determine the tracer diffusion coefficients of the components, using Darken - Manning approach coupled with Levenberg–Marquardt or genetic algorithm methods of optimization. The approach was also validated against literature data obtained for diffusion in Co-Cr-Fe-Ni-Mn alloys. The results for both systems confirm the theory of sluggish diffusion in High Entropy Alloys, with the values of diffusion coefficients being significantly lower than in the case of conventional alloys.