Surface pressure pi- and surface potential DELTAV area A isotherms for monolayers of alkylammonium perfluoroalkanoates of four different perfluoroalkyl chains on 4.4 M NaCl solutions were measured by the Langmuir method and the ionizing electrode method. The phase transition pressures pi(eq) change widely depending on the combination of hydrocarbon cation and perfluorocarbon anion lengths. Some pi-A curves of these long hydro-short fluoro salts exhibited two phase transition points. From the surface pressure and surface potential measurements, the orientation of the long hydro-short fluoro chain salts in the monolayer state was discussed.