High optical quality crystals of K2Al2B2O7 (KABO) up to 50 x 20 x 17 mm(3) in size and weight of 30 g have been grown using an improved top-seeded growth method with a NaF flux. The solubility data of KABO in NaF is reported over the temperature range of 920-790degreesC and the effect of seed orientations on the crystal growth is investigated. Seed along (110) direction is the best choice for the growth of this crystal. The quality of the crystals was evaluated by Synchrotron topography method and a D5000 high resolution X-ray diffractometer. The conversion efficiency of the fourth harmonic generation with a specimen 3.7 mm in length reached 12.3% for Q-switched Nd:YAG lasers. (C) 2002 Published by Elsevier Science B.V.