Cryogenic transmission electron microscopy was used to investigate the influence of counterions on viscosity for micelle solutions of C(8)F(17)SO(3)X (X = N(C2H5)(4), Li) pure and mixed with C10H21(OC2H4)(5)OH (C(10)EO(5)). Micrographs of micelle systems of pure C8F17SO3N(C2H5)(4) (FOSTEA) and in mixtures with C(10)EO(5) revealed the formation of threadlike micelles. With increasing concentration of FOSTEA, threadlike micelles formed a randomly looped structure. For mixed surfactant systems the formation of threadlike micelles with the looped structure was shifted to higher concentrations of FOSTEA. The formation of dense looped structures was attributed to the increasing viscosity with increasing concentration of FOSTEA. However, micrographs of micelle systems of C8F17SO3Li (FOSLi) including its mixtures with C(10)EO(5) only showed the formation of spherical micelles except for certain ratios of FOSLi/C(10)EO(5). These systems revealed no particular loop formation of micelles. This corresponded with a constant hulk viscosity close to that of water even for high concentrations of FOSLi. The different influence between tetraethylammonium and lithium counterions on the formation of threadlike micelles and spherical micelles was discussed in terms of the hydrophobic and hydrophilic nature of these ions.