A new non-centrosymmetric polyborate, Li₅Rb₂B₇O₁₄, has been synthesized. The structure of the title compound was solved by single-crystal X-ray diffraction analysis. The infinite three-dimensional structure of Li₅Rb₂B₇O₁₄ is constructed from bridged LiO_n (n = 4, 5, 6) and RbO₁₀ polyhedra with two kinds of one-dimensional B–O chain fundamental building blocks through their vertex oxygen atoms. It melts congruently and exhibits a short-wavelength absorption onset at 190 nm. The feature of a short UV cut off edge is favourable in practical applications. The calculated band structure and the density of states of Li₅Rb₂B₇O₁₄ suggest that its indirect energy gap is 4.247 eV. The materials have also been characterized by infrared spectroscopy and thermal analysis.