Generally, a slip casting process is closely related to the flocculation state of particles. The present investigation was undertaken in order to understand the relationship between the flocculation state of particles and the packing structure on the surface of gypsum mold.The flocculation state of particles in Al2O3-slurry was discussed on the basis of rheological behavior as a function of dispersant concentration. As the result, it was found that the type of rheological properties was classified into three modes.For these slurries, the absorbing rate and pressure of water and the increase of packing layer thickness were measured in order to explain the packing structure on the surface of mold. From these results, it was shown that the most suitable condition for slip casting could be prepared by using a weakly flocculated slurry.