The new orthorhombic meta-oxoborates RE(BO₂)₃ (≡REB₃O₆) (RE = Dy-Lu) have been synthesized under high-pressure and high-temperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 1100 °C. They are isotypic to the known ambient pressure phase Tb(BO₂)₃, space group Pnma. In contrast to Dy(BO₂)₃, which was also obtained in small amounts under high-temperature conditions, the preparation of the higher orthorhombic homologues RE(BO₂)₃ (RE = Ho-Lu) was only possible using high-pressure. The meta-oxoborates RE(BO₂)₃ (RE = Dy-Er) were synthesized as pure products, whereas the orthorhombic phases with RE = Tm-Lu were only obtained as byproducts. With the exception of Yb(BO₂)₃ it was possible to establish single crystal data for all compounds. The results of temperature-resolved in-situ powder-diffraction measurements, DTA, IR-spectroscopic investigations, and magnetic properties are also presented.