The evolution of the electronic structure of the intermetallic compounds ErNi5 − xAlx (x = 0, 1, 2) with different positions of the substitution of aluminum atoms for nickel atoms has been investigated. For this purpose, spin-polarized calculations of the energy band spectra of these compounds have been performed using the LSDA + U method, which in the local spin density approximation takes into account strong electron correlations in the 4f shell of the erbium ion. Variants of the substitution of aluminum atoms for nickel atoms in different crystallographic positions in the 3d sublattice have been considered. An analysis of the band structure has demonstrated that substitutional aluminum impurities lead to the formation of nonmagnetic nickel 3d states and to a significant decrease in the electron density of states at the Fermi level. A comparison of the total energies of the substitutional configurations has revealed that the occupation of the 3g positions by aluminum atoms is more energetically favorable.