Single crystals of K(3)Al(2)As(3)O(12), tripotassium dialuminotriarsenate(V), were obtained unintentionally by the reaction of KAsO(3) with a corundum crucible at 973 K. The asymmetric unit contains three K, two Al, three As and 12 O atoms. The structure of the title compound is isotypic with those of other K(3)M'(2)X(3)O(12) (M' = Al, Ga; X = P, As) structures and is made up of a three-dimensional network of corner-sharing [AlO(4)] and [AsO(4)] tetra-hedra. The three K(+) cations are located in channels running along the [100], [001], [101] and [10[Formula: see text]] directions, exhibiting different coordination numbers of 9, 8 and 6, respectively. All corresponding [KO(x)] polyhedra are considerably distorted.