Mechanical alloying (MA) of Fe-B alloy systems using a conventional ball mill has been performed. The structure change of Fe100−xBx for the composition range 10≤x≤90 has been investigated using X-ray diffractometry, thermal analysis, transmission electron microscopy, scanning electron microscopy and Mossbauer spectroscopy. According to the X-ray diffraction analysis, the sequences of transformation have been classified into three groups,x≤20, 25≤x≤35 andx≥50 for Fe100−xBx. The amorphous phase whose composition is nearlyx=30, first appeared for the whole composition range. This amorphous phase changed into a tetragonal Fe2B-like compound on further milling for 1000 h. On further milling of thex= 50 sample, the Fe2B compound phase disappeared and orthorhombic FeB compound appeared.