Single crystals of Rb2CaB8O26H24, a new noncentrosymmetric borate material, have been grown with sizes up to 8 9 5 9 3 mm(3) by the slow evaporation of water solution at room temperature. The structure of the compound was determined by single-crystal X-ray diffraction. It crystallizes in the orthorhombic system, space group P2(1)2(1)2(1) with a = 11.5288(3) angstrom, b = 12.6 334(4) angstrom, c = 16.6966(4) angstrom, Z = 4 and R-1 = 0.0405, wR(2) = 0.1043. Ultraviolet (UV)-vis spectrum transmission is performed on the Rb2CaB8O26H24, which shows an absorption edge about 195 nm in the UV region. Thermal properties were investigated by TG-DSC analysis. The powder second-harmonic generation (SHG) intensity measured by the Kurtz-Perry method indicates that Rb2CaB8O26H24 has about one-third of KDP (KH2PO4). The influence of different molar ratios and evaporation speed of water solution on crystal quality and size was also performed on the reported material.