A new noncentrosymmetric polyborate, Li6Rb5B 11O22, has been designed and synthesized in the Li 2O-Rb2O-B2O3 ternary system. The structure of the title compound was solved by single crystal X-ray diffraction analysis. It crystallizes in the monoclinic space group C2. The new structure contains an infinite three-dimensional matrix that is built from B 11O22 building blocks and LiOn (n = 4, 5), RbOn (n = 9, 10) polyhedra. The B11O22 building block has not been reported previously in any anhydrous and hydrated borates. The optical characterization of the compound indicates that its UV cutoff edge is below 190 nm. IR spectroscopy, thermal analysis, and second-harmonic generation were also performed on the reported material.