A new nonlinear optical material Gd x La 1−x Sc 3 (BO 3 ) 4 (GLSB) has been synthesized in the trigonal huntite-type structure. The composition parameter x, which defines the existence region of the trigonal huntite-type structure, was determined. Large single crystals were successfully grown by a high-temperature top-seeded solution growth method using Li 6 B 4 O 9 –LiF as a flux. Evidenced by single-crystal X-ray diffraction measurements, the member Gd 0.22 La 0.78 Sc 3 (BO 3 ) 4 crystallized in space group R32 with cell dimensions a=9.7933 and c=7.9540Å. The UV absorption edge for polished pieces exhibited at a wavelength shorter than 200nm. Sellmeier equations were established on the basis of the refractive indices measured by the auto-collimation method. The nonlinear optical coefficient d 11 was determined to be 2.08pm/V by the modeling and optical measurements of powders.