This paper reports about two new hydrogen-containing rare-earth oxoborates RE 4 B 6 O 14 (OH) 2 (RE=Dy, Ho) synthesized under high-pressure/high-temperature conditions from the corresponding rare-earth oxides, boron oxide, and water using a Walker-type multianvil equipment at 8GPa and 880°C. The single crystal structure determination of Dy 4 B 6 O 14 (OH) 2 showed: Pbcn, a=1292.7(2), b=437.1(2), c=887.3(2)pm, Z=2, R1=0.0190, and wR2=0.0349 (all data). The isotypic holmium species revealed: Pbcn, a=1292.8(2), b=436.2(2), c=887.1(2)pm, Z=2, R1=0.0206, and wR2=0.0406 (all data). The compounds exhibit a new type of structure, which is built up from layers of condensed BO 4 -tetrahedra. Between the layers, the rare-earth cations are coordinated by 7+2 oxygen atoms. Furthermore, we report about temperature-resolved in situ powder diffraction measurements, DTA/TG, and IR-spectroscopic investigations into RE 4 B 6 O 14 (OH) 2 (RE=Dy, Ho).