The integration of ferromagnetism with semiconductors to fabricate ferromagnetic semiconductors has been believed to be a potential way to make new spintronic devices. We have synthesized ferromagnetic Fe3Ga2-x As (x) nanoparticles in the surface of GaAs by employing ion implantation and rapid thermal annealing processes. Transmission electron microscopy revealed that these nanoparticles exist only in the top surface of the GaAs samples, with sizes from several to hundreds of nanometers. They have two orientation relationships to the GaAs matrix: [1 - 210](p)//[011](m), (10 - 10)(p)//(-42 - 2)(m) and (0002)(p)//(11 -1)(m); and [1 - 210](p)//[011](m), (-1010)(p)//(42 - 2)(m) and (0002)(p)//(-11 - 1)(m). The magnetic structures of the precipitates were studied by magnetic force microscopy. Results indicate that most of the ferromagnetic nanoparticles have single magnetic domains with their magnetic poles randomly orientated.