The amorphous alloys R4.5Fe77B18.5 (R=Pr, Nd) were prepared by melt-spinning technique under argon atmosphere on a cooper wheel rotating with surface velocity of 25 m·s-1. The ribbons have been investigated by means of X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Temperatures of crystallization for Pr 4.5Fe77B18.5, measured at the heating rate 20 K/min, are equal Tx1 = 591°C for the first exothermic effect and Tx2 = 603 °C for the second one (for Nd4.5Fe 77B18.5 Tx1 = 594 ° C and Tx2 = 633 °C). In the amorphous ribbons the crystallization of Fe3B phase in the first step, followed by the crystallization of Pr2Fe 23B3 and Nd2Fe23B3, was observed. Both later phases appear in the process of recrystallization, immediately after Fe3B formation.