The d4 configuration in an octahedral ligand field is considered. The optical absorption spectrum of Ru4+ is calculated by taking into account the ligand-field, electrostatic and spin-orbit interactions and using all the strong-field states of the ground configuration t 42 as well as those arising from the first excited configuration t32e. The matrix elements of the magnetic moment operator (L + 2S) were calculated between the ground state A1 and all the T1 states belonging to the two configurations. These matrix elements and the wavefunctions of the energy levels were used to calculate the magnetic susceptibility of Ru4+ in cubic coordination. It was found that the effect of the t32e configuration on both the energy levels and the magnetic susceptibility is very large and, therefore, cannot be ignored. The covalency of the t2 and e orbitals was also included in the calculations of the susceptibility. It was found that there is not much difference in the degree of covalency of these orbitals, and also the delocalization of the electrons is fairly small.