Wide Al-Ni polycrystalline ribbons were produced continuously via the planar flow casting(PFC) process. The influence of the process variables on the ribbon geometry has been investigated. The empirical correlation t_c＝0.835＾(0.32)/V_s＾(0.76) was proposed for the variation of ribbon thickness with melt flow reate and wheel velocity. The propagation rate(V) of the solid/liquid interface varies with the ribbon thickness(t), i.e. decreased with increasing the distance from the chilled surface of the ribbon, as V＝9.16t＾(－1). In accordance with the absolute stability criterion, the solid/liquid interface stability decreases as the solidification rate decreases toward the top surface of the ribbon, leading to the observed morphological degeneration, cellular to branched dendrite.