A high quality single crystal of K3B6O10Br has been grown with sizes up to 14 x 12 x 7 mm(3) by the top-seeded solution growth method. It crystallizes in a noncentrosymetric trigonal system, space group R3m with cell parameters a = 10.1153(8)angstrom, c = 8.8592(14)angstrom, Z = 3, V = 785.02(15)angstrom(3). K3B6O10Br has a three-dimensional network consisting of B6O13 units, which are surrounded by a K-Br framework. A transmission spectrum of the K3B6O10Br crystal was reported. Its refractive indices were measured by a minimum deviation technique and fit to Sellmeier equations. Nonlinear optical measurements demonstrate that the material has second harmonic generation properties, with efficiency approximately three times that of KH2PO4.