Small-angle neutron scattering experiments have been carried out on aqueous micellar solutions of mixed micelles of different tail lengths of cationic alkyltrimethylammonium bromide surfactants. It is found while the counterion condensation on mixed micelles is higher, the size of the mixed micelles lie in between those of the micelles of mixing components. The salt effect in mixed micellar systems confirms the formation of one type of micelles instead of two types of micelles formed by the individual surfactants. (C) 2003 Published by Elsevier Science B.V.