Using small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS), we have studied aqueous mixtures of fullerene-based ionomers. C-60[(CH2)(4)SO3Na](6) (FC4S), and sodium dodecyl sulfate (SDS). With the contrast variation provided by SAXS and a selected deuteration of SIDS for SANS, we have identified the formation of complex aggregates of FC4S and SIDS. The aggregation structure of the complex obtained is similar to that for pure FC4S aggregates and is stable to the SIDS concentration in the mixtures studied. Combining the contrast data sets of small angle scattering, we have obtained detailed aggregation information, including aggregation number, shape, size, and fractional ionization for the FC4S/SDS complex aggregates. It is found that the globular-like complex aggregate, with a radius of gyration of 20 Angstrom, consists of five FC4S and two SDS. in an average.