It was found for the first time that single tail ionic liquid (IL) surfactants, 1-alkyl-3-methylimidazolium bromides [C(n)mim]Br (n = 10, 12, 14), form unilamellar vesicles in aqueous solutions without any additives. With the increase in IL concentrations, the self-assembly of these ILs can transfer from spherical micelles to rodlike micelles and then to vesicles.