Single crystals of a new uranyl selenate (C6H16N2)[(UO2)2(SeO4)3(H2O)](H2O) have been prepared by isothermal evaporation from aqueous solutions. The crystal structure of a new compound has been solved by direct methods [monoclinic, P21/c, a = 11.3575(5) Å, b = 11.0210(5) Å, c = 17.8038(8) Å, β = 90.6080(10)°, V = 2228.39(17) Å3, Z = 4] and refined to R1 = 0.025 (wR2 = 0.055) for 4475 reflections with |Fo| ≥ 4σF using least square techniques. The structure is based upon the [(UO2)2(SeO4)3(H2O)]2- layers consisting of uranyl bypyramids sharing corners with selenate tetrahedra. The unique feature of this compound is the formation of organic cations [NH3-(CH2)3-C3H7N]2+ by combining broken and unbroken cyclic molecules.