The critical micelle concentrations (cmc’s) and solubilities of dodecylammonium perfluoroacetate (DAPA), perfluoropropionate (DAPP), and perfluorobutyrate (DAPB) were determined over the temperature range of 5-50 degrees C from electrical conductance measurements, and the effect of the extent of the hydrophobicity of the counterion on solubility, cmc, and the micellization temperature was examined. The degree of counterion binding to micelles of DAPA and DAPP was near 1.0. Their micellar sizes were found to be very large from the static and dynamic light scattering measurements. The mixed cmc’s were then determined for DAPA-DAPP, DAPA-DAPB, and DAPP-DAPB systems. The interaction between the perfluoro carboxylic acid anions in the mixed micellar state was investigated with use of the modified Rubingh’s equations, which take the dissociation of the counterion in an aqueous solution into account. The interaction between the counterions was found to be small and they mixed almost ideally in the micellar state. The crystal structure of these surfactants was determined by X-ray diffraction to be arranged obliquely.