For the purpose of examining the adsorption behavior of fluorine on clay minerals, the adsorption equilibrium experiments on fluorine were carried out using several clay minerals. Then various analysis and considerations, as listed in the followings, were done on the basis of the experimental results.<BR>1) The adsorbed amount of fluorine per unit mass of clay mineral was ranged as Kaolinite >Saponite >Pyrophyllite, Dickite >Montmorillonite.<BR>2) When the mass ratio of clay mineral to liquid was constant, the ratio of adsorption equilibrium concentration of fluorine to initial one became small, as the initial concentration of fluorine was lower.<BR>3) It was clear that there was less correlation between the BET specific surface area of the clay minerals and the adsorbed amount of fluorine, because the BET specific surface area was ranged as Saponite > Montmorillonite(Mikawa) > Kaolinite > Montmorillonite(Tsukinuno)> Dickite > Pyrophyllite. <BR>4) The cations such as the alkali metal (Na, K), alkaline earth metal (Ca, Mg), iron, silicon and aluminum, which are contained in the clay minerals, are major chemical components which may be bonded with fluorine. However the quantitative correlation between those each content in the clay minerals and the absorbed amount fluorine could not be recognized. <BR>5) For each clay mineral, the fluorine adsorption data can be arranged clearly in every conditions for the mass ratio of clay mineral to liquid. It was clarified the adsorption isotherm of fluorine on the clay minerals were represented using Freundlich's adsorption equation. <BR>6) The correlation equations which took the mass ratio of clay mineral to liquid into consideration were proposed on the adsorption coefficient and index in Freundlich's adsorption equation. Using both those equations and the values of adsorption parameters obtained in this study, it becomes possible to estimate the adsorbed amount of fluorine on the clay minerals and fluorine concentration in liquid phase.