Thin films of beta barium borate (β-BBO) have been prepared by liquid phase epitaxy on Sr2+-doped α-BBO (001) substrates. The thin films were characterized by X-ray diffraction and X-ray rocking curve. The results of X-ray diffraction indicate that the films show highly (00l) preferred orientation on (001)-oriented substrates. The full width at half-maximum of the rocking curve for the film is as low as 676.6 arcsec, which shows the high crystallinity of the thin film. The absorption edge of β-BBO on Sr2+-doped α-BBO substrate is 190 nm. The films show second harmonic generation of 400 nm light upon irradiation with 800 nm Ti: Sapphire femtosecond laser light. These results reveal the possibility of fabricating β-BBO (001) films on (001)-oriented Sr2+-doped α-BBO substrates by LPE.