[en] Moessbauer spectrometry, magnetization measurements and differential scanning calorimetry were used to investigate the microstructure and hyperfine interactions in the Fe_73.5Nb_4.5Cr₅CuB₁₆ nanocrystalline alloy obtained by heat treatment of the original amorphous precursor at the temperature of 550 deg. C for 1 hour. ⁵⁷Fe transmission Moessbauer spectra were taken in the temperature range 5-475 K without and with external magnetic field oriented parallel (H_ext approx. 0.05 T) and perpendicular (H_ext approx. 4 T) to the ribbon-shaped sample. The as-quenched state of the alloy was also investigated. The Moessbauer effect measurements confirmed the presence of α-Fe phase upon nanocrystallization. Magnetic states of Fe atoms in amorphous and interfacial regions are studied via distributions of hyperfine fields. (author)