The characteristics related to surface charge were investigated for various kind of kaolin minerals. Two types of kaolin minerals were used, one from weathering and sedimentary origins, Shinagawa-kibushi and Hara-gairome, and the other from hydrothermal origins, Georgia-kaolin and dickite. They were chemically treated in order to remove the organic species and ion-exchanged with Na⁺. The surface potential obtained from the variation of zeta potential and the cation exchange capacity (CEC) were studied for neutral kaolin minerals. A positive correlation exists between the surface potential and the CEC, and the CEC depends directly on the surface potential on the particle. The surface potential was larger for clays of weathering and sedimentary origins, Shinagawa-kibushi and Hara-gairome, than that of the hydrothermal originated Georgia-kaolin and dickite. The surface potential among kaolin minerals depends on the thickness of the edge plane and increases with a decrease in the crystallite size. Therefore, Shinagawa-kibushi and Hara-gairome which have large surface potential, have a large water film thickness due to the large amount of absorbed cations.