CP (Cetylpyridinium)-exchanged smectite was manufactured by the cationic exchange reaction of Na-smectite with CP. The adsorption behaviour shows a typical L-type isotherm representing continuous and stable adsorption in excess of twice the cation exchange capacity of CP. CP-smectite shows a strong interlayer (d001) expansion to 40.2 Å when an amount of CP equivalent to 140% of the CEC is exchanged into smectite. CP-smectite is characterized by strong alkalinity (pH 9.3), low swelling (4.5 ml/2 g), low viscosity (3.9 mPa s), and strong and fast flocculation. These characteristics are in striking contrast to Na-smectite except for the alkalinity. CP-smectite shows no signs of desorption of the organic species under varying pH conditions (pH 2–12). Desorption is slight even when washed three times with DH2O (distilled water). Pyrolysis of CP-smectite begins at 250°C and ends at 400°C. These stable and persistent characteristics and the relatively low price of CP point to the likely increased use of CP-smectite as an organoclay.