Two gallium-based borates, K3Ba3Li2Ga4B6O20F (I) and Rb3Ba3Li2Ga4B6O20F (II), have been successfully grown in the M2O (M = K, Rb)-LiF-B2O3 flux. They can be recognized as the element cosubstitutions of Sr for K/Rb and Ba and of Be for Li and Ga from Sr2Be2(BO3)(2)O (SBBO), which uses poisonous beryllium oxide during the synthesis and crystal growth process and also exhibits the problem of structural instability. The isostructural borates crystallize into the noncentrosymmetric space group P (6) over bar 2c, with a = 8.6398(12) angstrom and c = 16.827(3) angstrom for I and a = 8.7214(12) angstrom and c = 17.180(3) angstrom for II. In the structures, the basic anionic units are the BO3 triangles and GaO4 and LiO3F tetrahydra. These anionic units bond together through 0 atoms, forming the infinitely extended (2)(infinity)[LiGa2B3O12](8-) single layer at the ab plane. The adjacent layers are further coupled to the (2)(infinity)[Li(2)G(4)B(6)O(20)F](9-) double layers by means of bridged O and F atoms. Then the adjacent double layers are strongly joined together via O atoms of the GaO4 tetrahedra to form a three-dimensional skeleton, with K/Rb and Ba atoms occupying the network for charge balance. I and II have considerable second-harmonic-generation responses of about 0.7 and 0.5 as large as that of KH2PO4, respectively. In addition, the first-principles calculations were conducted to confirm that they address the structural instability issues in SBBO.