Magnetic annealing with a tunable solenoid magnetic field from 0-240 G, was conducted on a Bi-Pb-Fe-Cd-O glass containing 20% Fe2O3, which was prepared by the melt-quenching process. The crystalline phases of the annealed samples were identified as gamma-Bi2O3 and BiFeO3. Evidence of the formation of the crystalline BiFeO3 which was strongly magnetically enhanced at the surface of the samples, was obtained from X-ray diffraction patterns and EPR spectra. Based on the structure transition of Fe3+ ions, a crystallization mechanism for the BiFeO3 crystals under magnetic annealing has been proposed.