The structure and magnetic properties of (Nd1-xGdx)3Fe27.31Ti1.69 compounds have been investigated by means of X-ray diffraction and magnetic measurements. All compounds with x in the range of x≤0.6 crystallize in Nd3(Fe, Ti)29-type structure. Substitution of Gd for Nd leads to a contraction of unit-cell volume. The Curie temperature TC and anisotropy field Ba of the (Nd1-xGdx)3Fe27.31Ti1.69 compounds increases monotonically with increasing Gd content. Saturation magnetization Ms of the (Nd1-xGdx)3Fe27.31Ti1.69 compounds decreases with increasing x. As temperature lowers from room temperature to 5K, a spin reorientation from the easy plane to the easy cone occurs for (Nd1-xGdx)3Fe27.31Ti1.69 compounds. Spin phase diagrams have been constructed for (Nd1-xGdx)3Fe27.31Ti1.69 compounds.