New polymorphic variety of Ba(AsO3OH) has been obtained using hydrothermal method. Itrepresents one new structure type. Its crystal structure was determined from a racemic twin by single-crystal X-ray diffraction at 120 and 293 K [space group P21, a = 7.2149(14) / 7.2370(2), b = 7.7028(15) / 7.7133(2), c = 21.7385(43) / 21.8079 Å, b = 95.95(3) / 96.073(1)°, V = 1201.6(4) / 1210.51(5) Å³, Z = 12]. The structure refinement of the data collected at 120 K did not reveal significant changes and did not indicate any phase transition. The crystal structure of Ba(AsO3OH) has a layered character and can be divided into four types of regularly alternating layers parallel to (001). Each layer shares common O atoms and OH groups with adjacent layers. All these layers host different kinds of BaO7(OH)2 and BaO8(OH)2 polyhedra and isolated, slightly distorted AsO3OH tetrahedra. These tetrahedra are linked through three O atoms and one OH group to four Ba atoms in the same layer i.e. AsO3OH tetrahedra are chelating to two Ba atoms and bridged by another two Ba atoms. The OH group acts as hydrogen bond donor toward the oxygen atoms positioned in the same or adjacent layers. In all layers neighboring BaO7(OH)2 and BaO8(OH)2 polyhedra form zigzag chains along b-axis sharing edges or trigonal faces. These polyhedra are additionally connected by hydrogen bonds involving all hydroxyl groups. Raman and infrared spectra were acquired to obtain further information on both anion groups and especially on the very short hydrogen bond distances, where the donor and acceptor atoms are not equal due to (average) space-group symmetry.