We describe the spontaneous self-assembly and the superstructure of a discrete surfactant-encapsulated cluster, (DODA)(40)(NH4)(2)[(H2O)(n)subset of Mo132O372(CH3COO)(30)(H2O)(72)] (2, n approximate to 50), which consists of a hollow giant isopolyoxomolybdate core covered by a hydrophobic shell of dimethyldioctadecylammonium (DODA) cations. The structural characterization of these nanoporous core-shell particles is based on small-angle X-ray scattering (SAXS) data on solutions of the encapsulated clusters, TEM investigations, FT;LR and W-vis spectroscopy, as well as determination of the molecular area of 2 by Langmuir film investigations. Computer modeling of the solvent-accessible surface of the encapsulated cluster yields a central cavity with a volume of 1.5 nm(3) that is occupied by approximately 50 H2O molecules. The cluster bears (Mo-O) 9-ring openings with an average diameter of 0.43 nm. The covered surface area of 84 Angstrom(2)/DODA indicates a rather tight packing of the amphiphile at the cluster surface. Due to the unique supramolecular architecture of 2 as well as its high solubility in common organic solvents, this compound shows promising perspectives for future applications in host-guest chemistry and homogeneous size-selective catalysis.