Abstract We investigate the geometry and the electronic structure of Eu@C 60 by the scalar relativistic full-potential linear-combination-of-atomic-orbitals method based on the density functional theory within the local-spin-density approximation. It is found that the reaction Eu+C 60 → Eu@C 60 is exothermic with the reaction energy of about −3 eV. Eu is placed at about 1.2 Å away from the center of the C 60 cage. Two 6s electrons in Eu are transferred to the lowest-unoccupied-molecular orbitals of C 60 while seven 4f electrons remain in Eu. The Eu atom in Eu@C 60 thus exists as Eu 2+.