Three new galloborates, namely, GaB5O8(OH)(2)(en)(2)center dot H2O (1), LiGa(OH)(BO3)(H2O) (2), and Rb2Ga(B5O10)(H2O)(4) (3), have been synthesized by hydrothermal reactions. Compound 1 is the first example of a galloborate that contains an organic component. It crystallizes in space group P2(1)/c, and its crystal structure exhibits an infinite zigzag chain consisting of [B5O8(OH)(2)](3-) anions and GaO2N4 octahedra interconnected via corner sharing. Compound 2 crystallizes in space group P31c with a layered structure composed of GaO4, LiO4, and BO3 building units. Compound 3 belongs to chiral space group C222(1); the basic building blocks of the structure are the [B5O10](5-) cluster anion and GaO4 tetrahedron, which are interconnected to form a three-dimensional network with tunnels of Ga2B6 eight-membered rings (8-MRs) which are filled by Rb+ cations and lattice water molecules. Interestingly, Rb2Ga(B5O10)(H2O)(4) displays a moderate second-harmonic generation (SHG) response comparable to that of KH2PO4 (KDP), and it is phase matchable. Band structure and optical property calculations for Rb2Ga(B5O10)(H2O)(4) based on DFT methods were also performed.