Oxo-diketonate, Bi₃₈O₄₅(hfac)₂₄, that contains the largest known homometallic bismuth oxo-cluster, was isolated by aggregation of nonanuclear bismuth species in coordinating solvents. The crystal structure of this nanosized molecule revealed a giant [Bi₃₈O₄₅]²⁴⁺ core cluster with 24 β-diketonate ligands bound to its surface. Within the bismuth oxo-core a central [Bi₆] unit can be identified whose metal atoms are connected only to oxo-groups. All other 32 bismuth atoms are coordinated to both oxo- and diketonate ligands. The “internal” unit consists of an octahedron of bismuth atoms, each face of which is centered by an oxo-group. In addition, there is a unique µ₆-O atom residing in the middle of the octahedron, on an inversion center. Alternatively, the structure of the [Bi₃₈O₄₅]²⁴⁺ oxo-cluster can be described as assembled from 13 octahedral edge-sharing [Bi₆] units. The arrangement of bismuth atoms is close to an fcc structure in which all of the tetrahedral and some of the octahedral voids are occupied by oxygen atoms.