Powder and plastic body properties ground by stamp-mill(SM) or ball-mill (BM) were evaluated in the aim of improving the grinding process of Amakusa pottery-stone. SM powder had relatively large amounts (25-30 mass%) of particles both <1 mu m and >30 mu m in size. On the other hand, BM powder had relatively large amount (20-25 mass%) of particles 5-10 mu m and 10-20 mu m in size. Very fine particles (<1 mu m) in the SM powder contained much clay components compared to the BM powder. Shear stress in the BM clay body was larger than that in the SM clay body, when the water content was decreased. Therefore, the SMN body had higher fluidity than the BM body. It is supposed that the fluidity of the SM body was high because the friction between particles was low, as a consequence of the small size (<1 mu m) of the clay minerals. Grinding to larger amounts of fine clay minerals would be useful to reach high plasticity in the green body.