The electronic structures of CaCu 3Mn 4O 12 and CaCu 3Ti 4O 12 are investigated from HF SCF LCAO calculation. In CaCu 3Mn 4O 12, the band and the density of states show a spin asymmetric ferrimagnetic character with a small energy gap. The Mn spin is anti-aligned with the Cu spin, and the total spin moment is 9 μB. Our calculation correctly reproduces the observed antiferromagnetic insulating character of CaCu 3Ti 4O 12. The gap in the band structure, which is 2.15 eV, reasonably agrees with the experimental value 1.5 eV. The electron density populations at different planes show clearly that the electron density has symmetric character. A tilted Mn(Ti) orbital implies a typical tilted three-dimensional network of MnO 6 (TiO 6) octahedra due to doping of the Jahn-Teller ion Cu. There is no covalency between Ca, Cu and Mn(Ti) atoms. In contrast, there are stronger bonds and somewhat likely covalency between Cu and O atoms, and also between Mn(Ti) and O atoms.