Single crystals of Li3Cs2B5O10 have been synthesized and its structure determined by single-crystal X-ray diffraction. Li3Cs2B5O10 crystallizes in the non-centrosymmetric space group C222(1) ( No. 20). The structure consists of isolated B5O10 groups that are bridged by LiOn (n = 4, 5) and CsOn (n = 8, 10) polyhedra through their vertex oxygen atoms to form an infinite three-dimensional structure. Li3Cs2B5O10 melts congruently and exhibits a short-wavelength absorption onset at 175 nm. As-prepared Li3Cs2B5O10 is both non-centrosymmetric and phase matchable as supported by second harmonic generation measurements.