Single crystals with the composition KH3(SO4)(2) have been synthesized from the system Potassium sulfate/sulfuric acid. The hitherto crystallographically not investigated compound crystallizes in the monoclinic space group P2(1)/c (14) with the unit cell parameters a = 7.654(3), b = 11.473(5) and c = 8.643(3) Angstrom, beta = 112.43(3)degrees, V = 701.6 Angstrom(3), Z = 4 and D-x = 2.22 g . cm(-3). The structure contains two types of tetrahedra, SO3(OH) and SO2(OH)(2)). These tetrahedra form tetramers via hydrogen bonds consisting of both, two SO3(OH) and two SO2(OH)(2) tetrahedra. The tetramers are linked to each other via hydrogen bonds. Potassium is coordinated by 9 oxygen atoms which belong to both kinds of tetrahedra. These potassium oxygen polyhedra are connected by common faces forming chains running parallel z.