All salts studied effectively reduce critical micelle concentration(CMC) values of the cationic gemini surfactants. The ability to promote the surfactant aggregation decreases in the order of C6H5COONa > p-C6H4(COONa)(2) > Na2SO4 NaCl. Moreover, only C6H5COONa distinctly reduces both the CMC values and the surface tension at CMC. For 12-4-12 solution, the penetration of C6H5COO- anions and charge neutralization induce a morphology change from micelles to vesicles, whereas the other salts only slightly increase the sizes of micelles. The 12-4(OH)(2)-12 solution changes from the micelle/vesicle coexistence to vesicles with the addition of C6H5COONa, whereas the other salts transfer the 12-4(OH)(2)-12 solution from the micelle/vesicle coexistence to micelles. As compared with 12-4-12, the two hydroxyls in the spacer of 12-4(OH)(2)-12 promote the micellization of 12-4(OH)(2)-12 and reduce the amounts of C6H5COONa required to induce the micelle-to-vesicle transition.