A simulation of the evolution of the as-cast microstructure during the homogenization heat treatment of A6061 aluminum alloy is presented. The microstructure is dendritic with phase and solute segregation. The alloy microsegregation, which results after casting, was calculated with the Scheil equation by employing computational alloy thermodynamics. The microstructure evolution during homogenization was simulated by employing computational kinetics for the solution of the multicomponent diffusion equations. The composition profiles of the alloying elements and the volume fraction of the secondary phases were calculated as a function of homogenization time. The simulation results were validated qualitatively by comparison with metallographic examinations. During homogenization, the Mg2Si dissolution and the transformations of the Fe-intermetallics were confirmed. It is concluded that the model reproduces the homogenization kinetics reasonably and it is capable for the prediction of the homogenization heat treatment completion times.