In present work amorphous alloys Co48Fe25Si4B19Nb4-R (R = Nd, Sm, Tb, Yb) were obtained by planar flow casting in the form of ribbons with 3-5 mm wide and 35-45μm thickness. It was found that crystallization process goes into two stages and depends on the used rare-earth addition and its content in the alloy by differential thermal analysis method. Glass-forming ability criteria were calculated. It is shown that paramagnetic Curie temperature of alloys in liquid state can be used as their a-priori criterion of glass-forming ability. Keywords: amorphous alloys, crystallization, glass-forming ability, differential thermal analysis, x-ray diffraction, rare-earth metals.\