Pure samples of colorless, air-stable Ba(BO₂OH) crystals were obtained from Ba(NO₃)₂ and H₃BO₃ under the ultra-alkaline conditions of a KOH hydroflux at about 250 °C. The product formation depends on the water-base molar ratio and the molar ratio of the starting materials. B(OH)₃ acts as a proton donor (Brønsted acid) rather than a hydroxide acceptor (Lewis acid). Ba(BO₂OH) crystallizes in the non-centrosymmetric orthorhombic space group P2₁2₁2₁. Hydrogen bonds connect the almost planar (BO₂OH)²⁻ anions, which are isostructural to HCO₃⁻, into a syndiotactic chain. IR and Raman spectroscopy confirm the presence of hydroxide groups, which are involved in weak hydrogen bonds. Upon heating in air to about 450 °C, Ba(BO₂OH) dehydrates to Ba₂B₂O₅. Moreover, the non-centrosymmetric structure of Ba(BO₂OH) crystals was verified with power-dependent confocal Second Harmonic Generation (SHG) microscopy indicating large conversion efficiencies in ambient atmosphere.