The search of novel second-harmonic generation crystals in gallium selenite systems results in three new compounds of MGa2(SeO3)(4) (M = Sr, Pb) and BiGa(SeO3)(3). The isostructural MGa2(SeO3)(4) (M = Sr, Pb) are centrosymmetric (P (1) over bar, no. 2). The structures represent a complicated three-dimensional skeleton containing two different types of Ga4Se4 8-member polyhedral ring tunnels with the counter cations located at the broad ones. When the divalent counter cations were substituted by a trivalent lone pair cation of Bi(III), a novel noncentrosymmetric compound of BiGa(SeO3)(3) was achieved. BiGa(SeO3)(3) displays a 3D gallium selenite framework with 1D bismuth oxide chains filling in the 12-member polyhedral ring tunnels. Frequency doubling measurements showed that BiGa(SeO3)(3) presented an apparent SHG signal comparable to the commercial KDP and can realize phase matching. The lone pair anionic groups of SeO32- made the major contribution according to the SHG density analyses. BiGa(SeO3)(3) exhibits a wide transparent range and large optical bandgap (3.90 eV). The laser-induced damage threshold of BiGa(SeO3)(3) was estimated to be 98.68 MW/cm(2), about 44 x AGS.