Structural and magnetic properties of (Nd1-xRx)3Fe27.31Ti1.69 compounds with R = Dy or Er have been investigated by means of x-ray diffraction andmagnetic measurements. All compounds with x⩽0.5 for R = Er or with x⩽0.6 for R = Dy crystallize in Nd3(Fe, Ti)29-type structure. Substitution of Er orDy for Nd leads to a contraction of unit-cell volume. The Curietemperature TC of (Nd1-xDyx)3Fe27.31Ti1.69 compounds increases almost linearly withincreasing Dy content, whereas TC of the (Nd1-xErx)3Fe27.31Ti1.69 compounds decreasesmonotonically with increasing Er content. Saturation moments Ms of the(Nd1-xRx)3Fe27.31Ti1.69compounds decrease with increasing x for both R = Er andDy. As temperature lowers from room temperature to 5 K, a spinreorientation from the easy plane to the easy cone occurs for (Nd1-xErx)3Fe27.31Ti1.69 and two spinreorientations from the easy plane to two different easy cones occur forthe (Nd1-xDyx)3Fe27.31Ti1.69compounds. The anisotropy field Ba at room temperature for(Nd1-xDyx)3Fe27.31Ti1.69compounds increases with increasing Dy content, whereas Ba for(Nd1-xErx)3Fe27.31Ti1.69compounds decreases with increasing Er content. Spin phase diagrams havebeen constructed for both (Nd1-xDyx)3Fe27.31Ti1.69 and (Nd1-xErx)3Fe27.31Ti1.69 compounds.