Oxygen radical treatment was applied to sputter-deposited BiFeO3 (BFO) thin film which is expected to be used for ferroelectric memories, sensors and solar cells. The oxygen radicals were produced by a microwave excited high-density Kr/O2 plasma. It was found from X-ray diffraction (XRD) that the crystallization temperature of the BFO film could be reduced to 350 °C by applying the oxygen radical treatment before the annealing. The (110) peak area which shows the crystallinity of BFO was by 4 times than that of the BFO film annealed at 500 °C without the oxygen radical treatment. From results of XRD and X-ray photoelectron spectroscopy (XPS), the stoichiometry was dramatically improved and this suggests that the oxygen radical treatment effectively creates the nucleation cites of BiFeO3 and reduces oxygen vacancy defects.