Single crystals of a new uranyl carbonate (NH4,Na)4[UO2(CO3)3] (1) have been prepared by evaporation at room temperature from aqueoussolution. The structure was solved by direct methods [orthorhombic, Cmcm, a = 15.712(3), b = 9.039(2), c = 8.915(3) Å, V = 1266.2(6) Å3 and Z = 4] and refined to R1 =0.0314 (wR2 = 0.0704). The crystal structure of the novel compound is based on pseudo-layered complexbuilt by [(UO2)(CO3)3]4– uranyl tricarbonate clusters (UTC) linked together through Na+ and NH4+ ions. Such layered complexes of UTC are typical for a number of uranyl compounds of both natural and synthetic origin, including čejkaite. However, the relative arrangement of layers in 1 is distinct due to the specific interlayer content and can be described as a novel polytype.