The reaction of UO2(NO3)(2).6H(2)O with CS2CO3 or CsCl, H3PO4, and Ga2O3 under mild hydrothermal conditions results in the formation of Cs-4[(UO2)(2)(GaOH)(2)(PO4)(4)].H2O (UGaP-1) or Cs[UO2Ga(PO4)(2)] (UGaP-2). The structure of UGaP-1 was solved from a twinned crystal revealing a three-dimensional framework structure consisting of one-dimensional (1)(infinity)[Ga(OH)(PO4)(2)](4-) chains composed of corner-sharing GaO6 octahedra and bridging PO4 tetrahedra that extend along the c axis. The phosphate anions bind the UO22+ cations to form UO7 pentagonal bipyramids. The UO7 moieties edge-share to create dimers that link the gallium phosphate substructure into a three-dimensional (3)(infinity)[(UO2)(2)(GaOH)(2)(PO4)(4)](4-) anionic lattice that has intersecting channels running down the b and c axes. Cs+ cations and water molecules occupy these channels. The structure of UGaP-2 is also three-dimensional and contains one-dimensional (1)(infinity)[Ga(PO4)(2)](3-) gallium phosphate chains that extend down the a axis. These chains are formed from fused eight-membered rings of corner-sharing GaO4 and PO4 tetrahedra. The chains are in turn linked together into a three-dimensional (3)(infinity)[UO2Ga(PO4)(2)](1-) framework by edge-sharing UO7 dimers as occurs in UGaP-1. There are channels that run down the a and b axes through the framework. These channels contain the Cs+ cations. Ion-exchange studies indicate that the Cs+ cations in UGaP-1 and UGaP-2 can be exchanged for Ca2+ and Ba2+. Crystallographic data: UGaP-1, monoclinic, space group P2(1)/c, a = 18.872(1), b = 9.5105(7), c = 14.007(1) A, beta = 109.65(3)degrees, Z = 4 (Ts = 295 K); UGaP-2, triclinic, space group P1, a = 7.7765(6), b = 8.5043(7), c = 8.9115(7) A, alpha = 66.642(1)degrees, beta = 70.563(1)degrees, gamma = 84.003(2)degrees, Z = 2 (T = 193 K).