Abstract The agglomerated Al2O3 powders with the primary particle size of 43–570 nm were dispersed into aqueous solvent by wet-jet milling process. The agglomerations in low solid-loaded suspensions were completely pulverized by wet-jet milling and the average particle sizes were in good agreement with primary particle size. These sizes were increased with increasing solid loading. To evaluate the change of these sizes, the average surface to surface separation distance between particles (SDP) was calculated. The SDP decreased with increasing solid loading, and became constant at about 10 nm. At higher solid loading, particles were agglomerated in order to keep SDP at about 10 nm. These results indicate the dispersion and agglomeration of the particles strongly related to SDP.