THE ASYMMETRIC UNIT OF THE TITLE COMPOUND [SYSTEMATIC NAME: benzamidinium 3,3',5,5'-tetra-hydr-oxy-1,1'-spirobi[2,4,6-trioxa-1,3,5-triboracyclo-hexa-ne](1-) sesquihydrate], C(7)H(9)N(2) (+)·B(5)H(4)O(10) (-)·1.5H(2)O, is composed of two protonated benzamidinium cations, two tetra-hydro-penta-borate anions and three water mol-ecules of crystallization. The ions and water molecules are associated in the crystal structure by an extensive three-dimensional hydrogen-bonding network, which consists mainly of cation-to-anion N-H⋯O and anion-to-anion O-H⋯O hydrogen bonds.