The ceramic forming process can be considered as a condensation and dehydration process, and the condensation process can be simulated by the sedimentation test under gravity or centrifugal acceleration. To investigate the condensation and compression process more fundamentally, the submicron meter alumina powders were dispersed in distilled water with polyacrylic ammonium to prepare the 20-35 vol% slurries. The following three types of slurries were prepared by changing the concentration of polyacrylic ammonium; the coagulated, well dispersed and weakly coagulated slurries. The apparent viscosity of the slurries and the depth of the clarification zone under gravity were measured. Comparing the results of the apparent viscosity and the packing volume fraction, the following are elucidated. (1) The apparent viscosity and the sediment packing volume fraction change suddenly at different dispersant concentrations. It does not mean that well-dispersed slurry changes always to well-condensed sediment, (2) Changes in the final sediment packing fractions can be correlated with change in the dispersant concentration not the apparent viscosity. (3) It seems that the polymer dispersant functions as a lubricant during sedimentation and compression.