Polycrystalline series of single phase Nd1-xGdxCo4Si (0 <= x <= 1) solid solutions were prepared and characterized by X-ray powder diffraction (XRPD) and magnetization measurements. The powder X-ray diffraction patterns show that all samples crystallize as a single phase having the hexagonal CaCu5-type structure. The substitution of Gd for Nd leads to a decrease of the unit cell parameters a and c, and the unit cell volume V. Magnetic measurements indicate that all samples are ordered magnetically below the Curie temperature. The saturation magnetization at 4.2 K decreases upon the Gd substitution up to x = 0.6, and then increases. (C) 2009 Elsevier B.V. All rights reserved.