Cs2[(UO2)2(C2O4)3] (I) and Cs2[UO2(C3H2O4)2] · H2O (II) have been synthesized and studied by X-ray diffraction. The crystals of complexes I and II are monoclinic: a = 8.1453(2) Å, b = 8.9831(2) Å, c = 11.3897(4) Å, β = 104.0950(10)°, V = 808.29(4) Å3, space group P21/n, Z = 2, and R 1 = 0.0255 for I and a = 9.6998(2) Å, b = 17.8686(3) Å, c = 8.2074(2) Å, β = 97.5780(10)°, V = 1410.10(5) Å3, space group P21/c, Z = 4, and R 1 = 0.0287 for II. The uranium-containing structural units of complexes I and II are [(UO2)2(C2O4)3]2− chains and [UO2(C3H2O4)2] 2 4− dimers, which belong to the AK 0.5 02 T11 and AT11B01 crystallochemical groups (A = UO 2 2+ , K02 and T11 = C2O 4 2− , T11 and B01 = C3H2O 4 2− ) of uranyl complexes.