The optical and magneto-optical properties of single-crystalline GdFe 2 and GdCo 2 were measured by ellipsometry and magneto-optical Kerr effect spectroscopy in the 1.4-5.3eV range. The optical constants of the compounds are quite similar to each other in the whole energy range. On the other hand, their magneto-optical constants behave differently from each other with the structural peaks for GdCo 2 shifted to higher energies by about 0.5eV from those for GdFe 2 . The results indicate that magneto-optical measurements can detect differences in the electronic structure between the two compounds while optical measurements cannot. The peak shift is interpreted as due to a stronger d hybridization in GdCo 2 than in GdFe 2 , leading to larger d-state binding energies for GdCo 2 than those for GdFe 2 .