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 LiOn (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.