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The effect of the substitution of Sm, Nd and Ce for Gd on the structure and magnetic properties of (Gd1-xRx)(3)Fe28Nb (R = Sm, Nd and Ce) compounds have been studied. The single-phase regions for R = Sm, Nd and Ce correspond to thr composition range of 0 less than or equal to x less than or equal to 0.2, 0 less than or equal to x less than or equal to 0.5 and 0 less than or equal to x less than or equal to 0.4, respectively. All of the compounds crystallize in the Nd3Fe29-xTix-type structure. The lattice parameters a, b, c and V increase with the increase of the Sm and Nd content, while decrease with an increase of the Ce content. Substitution of Sm, Nd and Ce for Gd leads to a decrease of Curie temperature (Tc) and an increase of the saturation magnetization (M-s). The compounds (Gd1-xSmx)(3)Fe28Nb and (Gd1-xNdx)(3)Fe28Nb exhibit planar anisotropy perpendicular to the [102] direction, the anisotropy field HA increases with the substitution content, while in compounds (Gd1-xCex)(3)Fe28Nb, the planar anisotropy field H-A decreases with an increase of the Ce content. (Gd0.6Ce0.4)(3)Fe28Nb exhibits an intermediate easy axis behaviour.