A complex core-shell cluster consisting of 68 uranyl peroxo polyhedra, 16 nitrate groups, and similar to 44 K+ and Na+ cations was obtained by self-assembly in alkaline aqueous solution under ambient conditions. Crystals formed after a month and were characterized. The cluster, designated as {U1CU28CU40R}, contains a fullerene-topology cage built from 28 uranyl polyhedra. A ring consisting of 40 uranyl polyhedra linked into five-membered rings and 16 nitrate groups surrounds this cage cluster. Topological pentagons in the cage and ring are aligned, and their corresponding rings of uranyl bipyramids are linked through K+ cations located between the two shells. A partially occupied U site is located at the center of the cluster. Time-resolved small-angle X-ray scattering and electrospray ionization mass spectrometry demonstrated that the U-28 cage cluster formed in solution within an hour, whereas the U-40R shell formed around the cage cluster after more than several days.