A monoclinic crystal of BiB3O6 With dimensions of 44 x 24 x 10 mm(3) has been grown by the top-seeded method. The wavelength range of transparency is presented for the first time. Optical-quality BiB3O6, 0.2 mm thick, was transparent in the range of 270-6250 nm. Second-harmonic-generation (SHG) experiments were carried out on the samples along (theta = 168.9 degrees, phi = 90 degrees) the phase-matching direction in the (0 1 0) plane. A 3.0 mm long KTP sample was used for comparison. While 3.0 mm KTP has 46% SHG efficiency, the SHG conversion efficiency of a 2.3 mm long sample for 1.064 mum light was 67.7% at 6.2 mJ single pulse input energy. To the best of our knowledge, this is the highest SHG efficiency ever found for such a short length in the penetrating-light direction among SHG, nonlinear optical materials now widely used, such as KTiOPO4 (KTP), beta -BaB2O4 (BBO) and so on. Third-harmonic generation of a Na:YAG laser was obtained by using KTP as an efficiency converter.