In this article macrosegregation phenomenon is investigated by a finite volume numerical modeling technique and by upward unidirectional solidification of an Al-23 wt%Sn alloy casting. The numerical model consists of an explicit/implicit time integration scheme to couple thermal and solutal fields. The experimental solidification set-up allows a vertically aligned macrostructure to be obtained. The concentration profile was obtained by an X-ray fluorescence spectrometry technique carried out in cylindrical slices representing certain position inside the casting from the casting/chill interface. The simulated and experimental temperature and concentration profiles are compared and very good agreement has been observed. (C) 2008 Elsevier B.V. All rights reserved.