The interfacial tension of the hexane solution of 1,1,2,2-tetrahydroperfluorododecanol (FC12OH) against water was measured as a function of temperature and concentration under atmospheric pressure, The break point indicating a phase transition of the adsorbed him was seen on the interfacial tension vs temperature and concentration curves, The thermodynamic quantity changes associated with the adsorption were evaluated by applying thermodynamic relations; they were observed to change discontinuously at the transition point, By comparing this behavior with that of tetradecanol and octadecanol, the adsorbed film of FC12OH was concluded to be transformed from a gaseous to a condensed state.