The size and shape of novel partially fluorinated gemini surfactant 1,2-bis[dimethyl-(3-perfluoroalkyl-2F hydroxypropyl) ammonium] ethane bromide ((CnC3)-C-F-2-C3CnF, where n = 4, 6, and 8) were investigated in aqueous solution by means of light scattering and transmission electron microscopy (TEM). The sizes of these molecular aggregates changed with increasing carbon number of the alkyl chain and concentration. For example, the apparent hydrodynamic radius by dynamic light scattering was 18 nm at a concentration of cmc x 5 for n = 4, 115 urn at the cmc x 15 for it = 6, and 62 nm at the cmc x 30 for it = 8, at 298.2 K. The shapes of C-n(F) C-3-2-C3 C-n(F) aggregates drastically changed with the alkyl chain length; the aggregates were mainly in the form of large or irregular small auureaates (n = 4), string-like aggregates (n = 6), and vesicles (n = 8). The bromide-ion activity was measured using a bromide-ion-selective electrode to determine the degree of counterion binding to the aggregates. The degree of counterion binding to aggregate was very small compared with that in the typical hydrogenated gemini surfactants. These results indicated that the small curvature of large aggregates was not influenced by an electrostatic repulsion between the cationic head groups in the case of the bulky molecular volume of fluorinated gemini surfactants.