In this article the influence of the mushy zone permeability on the prediction of macrosegregation and mesosegregation (e.g. channel type segregation) has been studied using three different permeability laws. The three permeability laws have similar permeability in the inner part of the mushy zone (low liquid fraction regions), however, in the outer part of the mushy zone (high liquid fraction regions) permeability differs significantly. Simulations are performed for the solidification of a Sn–Pb alloy in a two-dimensional rectangular cavity using the three permeability laws and the effects of differences in these laws in the outer part of the mushy zone on macro- and meso-segregation are studied. We notice a sensitivity of the predicted macro- and meso-segregation, and of the width and shape of the mushy zone to various permeability laws. The sensitivity of the prediction of mesosegregates is much stronger than that of macrosegregation predictions. The value of the microstructural parameter used in the permeability laws plays an important role on the intensity of the macrosegregation and the nature of channel segregates with regard to their number, length and orientation. It has been observed that the permeability in the outer part of the mushy zone plays a key role in the formation of channel segregates.