In this paper, we studied the effect of heat treatment on the structural features and crystallization kinetics process of rapidly quenched Finemet-type ribbon for composition with 10% of iron substitution by manganese in initial state. After ribbon annealing at 580 °C for 30 min, and also at 600 °C for 10 and 30 min, the Fe(Si), Fe3B and Fe23B6 phases were identified. The crystallization activation energy, Ea, was found 585 kJ/mol (6.06 eV/at), and the Avrami exponent, n, was determined to be 3.13. In contrast to classical Finemet, where the crystallization process is a typical diffusion-controlled three-dimensional growth at a constant nucleation rate, in the modified alloy with 10% manganese, the growth of small particles predominates with an increase in the nucleation rate. During heat treatment the surface roughness and average peak height were increased from 3.0 to 24.2 nm and from 4.5 to 75.2 nm, respectively.