Comminution of kaolin clay samples, using attrition-milling in a stirred bead mill and high energy kneading in a pug-mill, was investigated at laboratory scale. Attrition-milling was shown to provide predominant delamination within the first minutes, prolonged treatment resulted in more marked transverse breakage of clay flakes. Pug-milling caused simultaneous delamination and breakage of clay platelets with dominant production of ultra-fine particles in the -0.5 mu m size range. When compared with feed and attrition-milled materials, pug-milled clays exhibit lower viscosity in relation with finer size distributions and lower aspect ratios (AR).