A single crystal of the new noncentrosymmetric material Cs 2 Ca[B 4 O 5 (OH) 4 ] 2 ·8H 2 O has been grown by a slow evaporation method with sizes up to 10×10×5 mm 3 using an aqueous acetone solution as a solvent. The crystal structure of this compound was determined by single crystal X-ray diffraction. It crystallizes in the Orthorhombic space group P2 1 2 1 2 1 with lattice parameters a =11.5158(7) A, b =12.8558(7) A, c =16.7976(10) A and Z =4. The optical transmittance spectrum was measured on the Cs 2 Ca[B 4 O 5 (OH) 4 ] 2 ·8H 2 O crystal, which exhibits an absorption edge at about 190 nm in the UV region. The powder second-harmonic generation (SHG) measurement indicates that Cs 2 Ca[B 4 O 5 (OH) 4 ] 2 ·8H 2 O is phase-matchable and the signal is about half that of a KDP (KH 2 PO 4 ) standard. Theoretical calculation shows it has moderate birefringence, and identifies the contribution of cations to the optical properties.