Nonlinear optical crystal of CaN 2 B 8 O 26 H 32 has been grown with sizes up to 9×8×5mm 3 by the solvent evaporation method. The structure was determined by single-crystal X-ray diffraction and further characterized by powder X-ray diffraction and IR spectrum analysis. CaN 2 B 8 O 26 H 32 crystallizes in the orthorhombic system, space group P2 1 2 1 2 1 , with unit-cell parameters a=11.556(7)Å, b=12.583(8)Å, c=16.679(8)Å, Z=4, V=2425.2(2)Å 3 , R 1 =0.0263, and wR 2 =0.0655. The structure is made up of CaO 7 polyhedra, and [B 4 O 5 (OH) 4 ] 2− polyborate anions, NH 4 + cations, and H 2 O molecules. UV–vis–NIR diffuse reflectance spectrum is performed on the CaN 2 B 8 O 26 H 32 , which shows an absorption edge <190nm in the UV region. Thermal properties were investigated by TG analyses. The powder second-harmonic generation intensity measured by the Kurtz–Perry method indicates that CaN 2 B 8 O 26 H 32 has about half times that of KH 2 PO 4 .