The emulsion method was used to prepare nanocrystalline Ni0.7Mn0.3GdxFe2-xO4 ferrites. The growth of particles, the structure and the magnetic properties were investigated by X-ray diffraction (XRD), Mossbauer spectroscopy and vibrating sample magnetometer (VSM). Furthermore, the influence of Gd2O3 on magnetic properties of Ni-Mn ferrite powders has been investigated in detail. When the crystallite sizes are about 30-40 nm, all the samples have the similar Ms values. The variational rules of saturation magnetization (Ms) and coercivity (Hc) along with doped-Gd contents at different sintering temperatures show that the maximum Gd ions content doped into ferrite lattices is x = 0.06. When Gd-doped content x is larger than 0.06, the doped Gd ions can't enter into the ferrite lattice totally but reside at grain boundary, as the ionic radii of the Gd3+ ions are larger than that of Fe3+ ions. The ferrimagnetism have not disappeared completely, even if the crystallite size is 7.8 nm. (c) 2006 Springer Science + Business Media, Inc.