Using hydrothermal techniques, two new compounds—strontium borate SrBO₂(OH) and barium polyborate Ba₃B₆O₉(OH)₆—have been prepared. The structures of the title compounds were solved by single-crystal X-ray diffraction analysis. In the structure of SrBO₂(OH), the Sr²⁺ ion is surrounded by eight oxygen atoms and the borate ion is identified as an individual [BO₂(OH)]²⁻ group. The structure of Ba₃B₆O₉(OH)₆ can be regarded as constructed from anionic borate chains, the negative charges of which are compensated for by the Ba²⁺ cations residing between the adjacent chains. The unusual feature of this compound can also be described in terms of infinite chains of B₃O₃ six-membered rings sharing B atoms, which are all tetrahedrally coordinated by oxygen atoms. The materials have also been characterized by infrared and energy dispersive spectroscopies, thermal analysis, and second harmonic generation powder measurement.