The heterogeneous nucleation process of NH4CI crystals from a NH4CI-70wt.％H2O solution on rough chilling substrates was considered in this paper.Scratched and etched substrates of aluminum were prepared with different surface morphologies.It was concluded that for nucleation to occur on a rough substrate surface,the wettability or the generally said roughness are not the key factors affecting the heterogeneous nucleation process.Rather the surface morphologies on the nanometer scale,which is close to the scale of the critical nucleation radius,are more important.