The amorphous alloys R_4.5Fe₇₇B_18.5 (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 _4.5Fe₇₇B_18.5, measured at the heating rate 20 K/min, are equal T_x1 = 591°C for the first exothermic effect and T_x2 = 603 °C for the second one (for Nd_4.5Fe ₇₇B_18.5 T_x1 = 594 ° C and T_x2 = 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.