The crystal β-BaB 2O 4 is a new type of polar crystal of great practical value, which had not been discovered before. It is an excellent nonlinear optical material possessing good pyroelectric properties. The growth of β-BaB 2O 4 single crystals by flux seeding and flux pulling methods is described in this paper. It is shown from our experiments that the former is preferable to the latter for its growth. The efforts made to seek the best flux for the growth of this crystal are also described in detail. The liquidus temperature curves and the spontaneous crystallization temperature curves of three systems, i.e. BaB 2O4−BaF 2, Ba Bin2 O 4−BaCl 2 and BaB 2O 4−BaB 2O 4·Na 2O, are given. Large transparent crystals with a size up to 76 mm in diameter and 15 mm thick have been grown by the flux seeding method combined with slow cooling. These were cut into several pieces to make SHG (second harmonic generation) devices.