Differential scanning calorimetry has been used to study the kinetics of crystallization of Fe80Si4B16 metallic ribbon. Continuous heating and isothermal measuring techniques were used. Two overlapping exothermal peaks were always observed. Both processes proceeded by Johnson-Mehl-Avrami crystallization kinetics having temperature- and time-dependent activation energies. In the first crystallization step E(1)*(755 K) = 325 kJ (g atom)(-1) continuously increased to E(1)*(794 K) = 487 kJ (g atom)(-1) and the exponent n(1) = 2.5 decreased to 1.5 for extended degrees of conversion. These observations were interpreted as crystallization of two types of primary product having quite different kinetics. In the second crystallization step the exponent n(2) = 4 and the activation energy E(2)* having the mean value of 340 kJ (g atom)(-1) decreased slightly with increasing temperature. These observations were interpreted as the crystallization of the metastable and stable eutectic phases.