In this study, we evaluated the importance of the relativistic effects on the optical and magnetic properties of cerocene and thorocene and its corresponding anions. The optimized molecular structures show D(8h) symmetry for all systems, in good agreement with the experimental data. Atomic charges were analyzed using different approaches (Mulliken, AIM, multipole, and NBO), and the results suggest that the net charge on the thorium is greater than on the cerium atom; however, none of the methodologies were able to predict the expected net charge Ce(III) and Th(IV) atoms. However, by an energy decomposition analysis, a significant electrostatic, ionic, interaction, ~58% and ~61%, was found between the metal and the COT(2-) rings, respectively. The calculated electronic excitations are underestimated in comparison with the experimental data, while the calculated EPR g-tensors are in agreement with previous theoretical and experimental data. Besides, the NICS analysis shows an increased ring electron delocalization due to the lanthanide and actinide metals.