High energy ball milling of Fe, Mn, Al and B powders has been used to prepare iron-based alloys, with nominal composition Fe60Mn10Al30-xBx, with x = 2, 4, 6, 8, 10. For comparison, alloys with the same composition have also been prepared by arc-melting. The effect of the B content on the microstructure and magnetic properties of the products has been studied by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometry and magnetic thermogravimetry. After milling for 20 h a Fe-Mn-Al solid solution with a bcc structure is formed. As the B content is increased, a decrease in the bcc cell parameter is found. Moreover, the appearance of new (Fe-Mn)(2)B phase becomes more evident for increasing B content. In addition, some superlattice peaks corresponding to the bcc phase are observed in the arc-melt samples. The alloys are found to be ferromagnetically soft. Two magnetic transitions are observed in ball-milled samples when the temperature is increased. The first one, which is associated to a magnetic transition in the bcc phase, is found to shift to higher temperatures as B content is raised. Changes in the Fe-Fe atomic distances in the bcc phase when changing B content are likely to be responsible for this magnetic behavior.