Fe-based amorphous and nanocrystalline alloys can be used for technological applications on iron core materials owing to their high permeability, low coercivity, and core loss. However, when compared to Si-steels, their application is limited owing to low saturation magnetization. Thus, the saturation magnetization of Fe-based amorphous and nanocrystalline alloys should be improved, which may reduce the content of metalloid elements, and thus, the amorphous forming ability. Consequently, as-spun Fe-based amorphous and nanocrystalline alloys with high saturation magnetization may be incompletely amorphous. In this case, annealing processes should be modified by investigating crystallization behavior because traditional annealing processes with low heating rates may degrade ferromagnetic exchange and soft magnetic properties owing to grain-size inhomogeneity. Fe₇₆Ga₅Ge₅B₆P₇Cu₁ ribbons were fabricated using the melt spinning technique, and their crystallization behavior and mechanism were studied. Results showed that two exothermic peaks are present in the DSC curve, which correspond to the precipitation of α-Fe(Ga, Ge) and Fe(B, P) phases. Under nonisothermal conditions, the initial activation energy is greater than the apparent activation energy. According to the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation, for an incomplete amorphous alloy, the crystallization process combines the growth of pre-existing nucleus and nucleation, whereas the nucleation rate decreases. Moreover, a rapid heating annealing process is conducive to the formation of a uniform and dispersed nanocrystalline structure. It was found that the magnetic properties of the annealed alloy with a heating rate of 100 K/min was better than those with 10 and 50 K/min. Further, the optimal initial permeability was 2.86 × 10^-2 H/m, and the coercivity was 1.77 A/m.