The hydrophilic and hydrophobic components of the surface of the hydrothermal kaolinite has been characterized using adsorption of passively and negatively charged surfactants in aqueous solution. The hydrophilic and hydrophobic surface areas are inferred from the amount of probe molecule adsorbed and the structure of the adsorbed layer. The hydrophilic structure area of kaolinite is estimated from the adsorption of cationic surfactant: benzyl-demethyl-dodecyl-ammonium bromide (BDDAB). The adsorption of anionic surfactant; sodium dodecyl sulfate (SDS) onto kaolinite surface particles has been performed to assess their hydrophobic surface area. The area of the hydrophobic parts of kaolinite was found to be 37 m².g^-1. The sum of the hydrophilic (1.42 m².g^-1) and the hydrophobic surface gives 38.42 m².g^-1, a value which is only 21 % smaller than BET surface area ( 48,7m².g^-1).