Lithium uranyl oxalate hydrate, Li2UO2(C2O4)(2) . 5H(2)O and sodium uranyl oxalate hydrate, Na2UO2(C2O4). 4H(2)O have been prepared and characterized by chemical and thermal analyses as well as X-ray diffraction and infrared spectroscopy. X-ray powder data show that the compounds belong to a monoclinic system. Thermal decomposition and infrared studies show that the compounds decompose to monouranates through the formation of alkali metal carbonates and UO2 as intermediates.