A gadolinium-rich borate Gd-17.33(BO3)(4)(B2O5)(2)O-16 was successfully grown by the high-temperature solution method using the Rb2O-B2O3 flux. The crystal crystallizes in centrosymmetric space group C2/m with lattice constants a = 18.4300(2) angstrom, b = 3.7400(4) angstrom, c = 14.2047(16) angstrom, and beta = 119.8550(12)degrees. Two different honeycomb-like [GdO] layers alternately arrange in the order ABAB forming the three-dimensional framework, in which the isolated [B2O5] and [BO3] units fill in channels of the 12-membered and 10-membered [GdO] polyhedral rings, respectively. The UV cutoff edge of Gd-17.33(BO3)(4)(B2O5)(2)O-16 is less than 240 nm. The maximum -Delta S-m,S-max is 26.53 J kg(-1) K-1 or 174.70 mJ cm(-3) K-1 (T = 4.4 K and Delta H = 7 T) as investigated by the isothermal magnetization method.