The lanthanum oxoborate is a material with a non-centrosymmetric structure which is important for optical and sensorical application. Sintering has been performed to find the best parameters to produce the polycrystalline phase free from phase shift to grow a single crystal. A slight excess of B2O3 is necessary because of the hygroscopic properties of boron oxide. A DSC measurement of the Ca-4 La[O vertical bar(BO3)(3)] was performed to determine the melting behaviour. LaCOB melts congruently at nearly 1410 degrees C. By using a [0 1 0] Ca4Gd[O vertical bar(BO3)(3)]-seed a single crystal of high quality had been produced by the Czochralski method. The grown crystal is free from macrodefects like bubbles and cracks with a typical shape of rhombohedral cross section. Single-crystal X-ray diffraction in combination with a powder diffraction measurement showed, that the structure belongs to the monoclinic system with space group Cm and a(0)=0.817079(8) nm, b(0)=1.608406(16) nm, c(0)=0.362844(3) nm and the angle beta = 101.352(1)degrees. The R-value for the solved structure is 0.0201. (C) 2011 Elsevier B.V. All rights reserved.