We report the preparation of amorphous Fe80-xCrxB20 (5 ≤ x ≤ 70) fine particles by chemical reduction, their morphological and structural characterization by SEM, TEM measurements and X-ray diffraction, and the study of their magnetic properties by means of Mossbauer and magnetization measurements. The particles are spherical and their size (10 < φ < 200 nm) is composition dependent, decreasing with increasing Cr-content. The magnetic properties, determined by chemical composition and by particle sizes distribution, move with increasing chromium content x, from a ferromagnetic character to a magnetically disordered state, characterized by the coexistence of ferro and antiferromagnetic interactions.