The structure and magnetic properties of the (Nd1-xErx)3Fe18Co6Cr 5 compounds with x = 0.0-0.8 have been investigated by means of x-ray diffraction and magnetic measurements. It is found that all the compounds are single phase and crystallize in the Nd3(Fe,Ti)29-type structure with monoclinic symmetry and space group A2/m. The lattice constants a, b and c and the unit-cell volume V show a tendency to decrease with increasing Er content, reflecting the lanthanide contraction. The Curie temperature decreases with increasing Er content. The spin-reorientation temperature Tsr increases with increasing Er content till x = 0.2, then tends to saturate upon further increase in Er content. The saturation magnetization at 5 K decreases with increasing Er content owing to the antiferromagnetic coupling between Er and Nd moments. A first-order magnetization process is observed for compounds with x = 0, 0.2 and 0.4 at critical field values of 8 T, 4.5 T and 3.5 T, respectively, applied along the hard magnetization direction.