Solution properties of lithium 1-perfluoroundecanoate have been studied by electroconductivity and membrane potential measurements. The degree of counterion binding to micelles was not precisely determined by the Corrin-Harkins plots. The aggregation numbers and the degrees of counterion binding over the temperature range from 288.2 to 313.2 K have been evaluated by a new method that combined the above two measurements and the mass-action model. The thermodynamic parameters of micellization were determined from the temperature dependence of the parameters obtained. The surfactant with a long perfluoroalkyl chain showed micellization properties much different from the corresponding hydrocarbon surfactant in that the temperature dependence of the aggregation number, the degree of counterion binding, the enthalpy change of micellization, and the entropy change of micellization are much greater.