The environment of the U atom in the title compound, (C(4)H(12)N)(4)[UO(2)(CO(3))(3)]·8H(2)O, presents a typical hexagonal bipyramidal geometry found in many actinide complexes. It is a model for actinide species and consists of common environmental moieties (carbonate, water and ammonia species). The structure displays a sheet-like hydrogen-bonding network formed from crystallization water molecules and carbonate ligands. The compound is isomorphous with a previously described Np isolog [Grigorev et al. (1997). Radiokhimiya (Russ. Radiochem.), 39, 325-329].