Abstract The effects of minor Nb addition on the crystallization mechanism for a FeNiPC(Nb) amorphous alloy were studied via investigating its non-isothermal crystallization kinetics. With minor Nb addition, the thermal stability of the alloy increases as evidenced by the enlargement of the supercooled liquid region. Meanwhile, the location activation energy of both Nb-added and without Nb-added alloys correlates positively with the crystallized volume fraction during the whole primary crystallization stages, as calculated by the isoconversional methods. However, the kinetics analysis using the modified Johnson-Mehl-Avrami-Kolmogorov equation indicates that the addition of Nb changes the crystallization mode of the alloys, that is, from the growth with a decrease nucleation rate to a constant nucleation rate in a diffusion-controlled manner. This can be further confirmed by the atomic force microscopy showing that Nb would restrain the atomic diffusivity and suppress the crystallization growth rate in this alloy.