The effect of manganese and carbon impurities on ribbon forming characteristics and crystallization behavior in Fe80.8 - xMnxB13.6Si5.6 - yCy has been studied. The source of these impurities was carbothermic ferroboron, iron powder or steel. Alloy 1 (x = 0.1, y = 0.2) gave good quality ductile ribbons of 35 +/- 2 mu m thickness, but Alloy 2 (x = 0.5, y = 2), with higher manganese, gave brittle ribbons. Differential scanning calorimetric studies on amorphous ribbons at different heating rates showed two-step crystallization for both alloys, i.e first alpha-Fe crystallizes, followed by tetragonal Fe3B at higher temperature. These phases were confirmed by X-ray diffraction and transmission electron microscopy. The effect of manganese content on peak temperatures was studied. Higher manganese content (0.5 a/o) increased the peak temperatures for the crystallization of alpha-Fe at all heating rates. This trend was not observed for the second peak at heating rates of 0 - 20 K/min. However; heating rates exceeding 20 K/min caused the same effect as observed in alpha-Fe. The activation energies for alpha-Fe crystallization were not affected by a higher manganese content. For the crystallization of Fe3B the activation energy was 299 kJ/mol for Alloy 1, which is lower than for 2605 SC or Alloy 2. The average and local Avrami exponents determined by isothermal annealing experiments were the same (approximate to 2.5) in both alloys for the first-stage crystallization. The average Avrami exponent was the same for the second stage of crystallization. The local Avrami exponent, which showed nonuniformity, indicates that multiple mechanisms for crystallization are operational.