Fe89.8Ni1.5Si5.2B3C0.5 undergoes multi-step structural transformations under thermal treatment. Crystallization process, occurring around 810K, was separated into two single-step processes, corresponding to formation of alpha-Fe(Si) and Fe2B crystalline phases, respectively. Significantly higher value of activation energy obtained for the first crystallization step indicate that formation of alpha-Fe(Si) facilitates the subsequent formation of Fe2B phase, by increasing in boron content of the amorphous matrix at the crystal/amorphous interphase boundary, while alpha-Fe(Si) crystallites probably serve as nucleation sites for crystallization of Fe2B phase. Narrow distribution of activation energies for both crystallization steps, obtained using Miura-Maki method, is an indicator of very homogenous structure of as-prepared amorphous alloy. The mechanism of formation of both crystalline phases was modeled using the general Sestak-Berggren model, and it was found that there is relatively small difference between respective reaction mechanisms, which is expected, as both phases crystallize directly out of the amorphous matrix. (C) 2013 Elsevier B.V. All rights reserved.