In this paper the unidirectional solidification methods and the microstructural investigation of Al-4wt.-%Cu alloys under non-steady-state conditions are reported. Influences of solidification process on the solidification parameters (temperature gradient, solid/liquid interface velocity) and on the microstructure are investigated. After melting the samples were moved downward into the water located under the furnace at three different decelerations. A computerised algorithm was worked out for the calculation of solid/liquid interface velocity and temperature gradient. These data were determined along the whole sample. The dendritic microstructure of samples formed during the solidification was analysed. The secondary dendrite arm spacing, the dendrite trunk diameter and the volume fraction of the second phase (Al2Cu) were measured by using the image analyser type Quantimet 500 Image Workstation.