Abstract: We report on the results of analysis of magnetic properties and electronic structure, which were obtained by self-consistent ab initio spin-polarized calculations, as well as experimentally determined optical properties of cobalt-based intermetallic compounds YCo3, Y2Co7, and LaCo5. Optical characteristics were measured using ellipsometry in a wide spectral interval. The mechanism of quantum absorption of light in these materials is considered based on comparative analysis of experimental and theoretical spectra of interband optical conduction. Analysis of the crystalline structure and the resultant magnetic, electronic, and optical characteristics revealed peculiarities in the variation of physical properties. which appeared upon an increase in the cobalt content in the intermetallides.