Fe-B nanoparticles were synthesized by using solution and reverse micelle methods. The structures, the B contents and the magnetic properties of the particles have been characterized by XRD, TEM, ICP, VSM, etc. It is found that the difference in magnetic properties of Fe-B nanoparticles fabricated by the two methods is mainly caused by the structure, the B content and the particle size. The Fe-B particles fabricated by solution method are crystalline with a size range of 20~70 nm, and the B content is about 17.8 at%; and the Fe-B particles prepared by reverse micelle method are usually non-crystalline with a size much smaller (about 5 nm), the B content is about 34.9 at%.