Crystalline beta barium berate (beta-BaB2O4) thin films have been successfully prepared in situ on several kinds of substrates by using opposed-targets magnetron sputtering. The crystallinity of these films is highly dependent on the deposition temperature. Crystalline films start to form at 500 degrees C and gradually become c-axis aligned as the temperature is increased. At 700 degrees C the film grown on sapphire substrates shows hundred-micrometer-sized domain structures with a single (006) x-ray diffraction peak normal to the film surface. For a linearly polarized fundamental beam incident along the surface normal, the second harmonic intensity exhibits a sixfold azimuthal pattern with a d(22) second harmonic coefficient of 1.2 pm/V.