Nd2Fe14B/alpha-Fe nanocomposites with a nominal composition of Nd8Fe86B6 (atomic ratio) were prepared by mechanically activated disproportionation of the as-cast alloy via ball milling in hydrogen, and a subsequent desorption-recombination treatment of the as-milled disproportionated alloy powders. The microstructure and morphology of both the as-milled and the subsequently desorption-recombination treated powders were characterized by X-ray diffraction (XRD), magnetic force microscopy (MFM), and transmission electron microscopy (TEM). It was found that milling in hydrogen for 20h led to complete disproportionation of the Nd2Fe14B phase in the as-cast alloy into a nano-structured mixture of Nd2H5, FeB, and alpha-Fe phases with average size of no more than 10nm. After a subsequent desorption-recombination treatment at 700 degrees C for 30min, the disproportionated alloy powders were completely turned into Nd2Fe14B/alpha-Fe nanocomposites with an average phase size of about 35nm, and powder size of about 130nm, respectively.