The effect of cooling rate in the solidification range and the development of the dendritic structure on the formation of nonequilibrium eutectics in Al-Cu alloys is investigated experimentally and by computer simulation. It is shown that 1D models cannot predict the experimentally observed dependences adequately since they do not take into account the development of the dendritic structure during solidification. The 2D models allow one to describe the process of solidification and the development of dendritic morphology more exactly and, as a result, predict dendritic liquation satisfactorily. It is revealed that a coarsening of the dendritic structure at the last stages of solidification in the rate range up to 20 K/s exerts the strongest effect on the formation of nonequilibrium eutectics.