Single crystals of the new uranyl selenate hydrate (C5H12NO)[(UO2)(SeO4)Cl(H2O)] (1) have been prepared by evaporation at room temperature from aqueous solution of uranyl nitrate, selenic acid, potassium hydroxide and choline chloride. The crystal structure of 1 has been solved by direct methods [monoclinic, P2(1)/n, a = 10.745(4), b = 11.236(4), c = 12.477(4) , beta = 114.580(5)A degrees, V = 1,369.9(8) (3), Z = 4] and refined to R (1) = 0.022 (wR (2) = 0.058) for 4,350 reflections with |Fo| a parts per thousand yen 4 sigma (F) using least square techniques. The structure is based upon the [(UO2)(SeO4)Cl(H2O)](-) layers consisting of UO6Cl pentagonal bypyramids sharing corners with SeO4 tetrahedra. The presence of the Cl- ions in the system leads to the formation of a mixed-ligand coordination of uranyl ions. The topology of the 2D layer in the structure of 1 is based upon 4- and 8-membered rings of polyhedra and is related to the one observed in the structure of apophyllite-group minerals.